--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mupdf-source/thirdparty/gumbo-parser/src/parser.c	Mon Sep 15 11:43:07 2025 +0200
@@ -0,0 +1,4188 @@
+// Copyright 2010 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Author: jdtang@google.com (Jonathan Tang)
+
+#include <assert.h>
+#include <ctype.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+#include <strings.h>
+
+#include "attribute.h"
+#include "error.h"
+#include "gumbo.h"
+#include "insertion_mode.h"
+#include "parser.h"
+#include "tokenizer.h"
+#include "tokenizer_states.h"
+#include "utf8.h"
+#include "util.h"
+#include "vector.h"
+
+#define AVOID_UNUSED_VARIABLE_WARNING(i) (void)(i)
+
+#define GUMBO_STRING(literal) \
+  { literal, sizeof(literal) - 1 }
+#define TERMINATOR \
+  { "", 0 }
+
+typedef char gumbo_tagset[GUMBO_TAG_LAST];
+#define TAG(tag) [GUMBO_TAG_##tag] = (1 << GUMBO_NAMESPACE_HTML)
+#define TAG_SVG(tag) [GUMBO_TAG_##tag] = (1 << GUMBO_NAMESPACE_SVG)
+#define TAG_MATHML(tag) [GUMBO_TAG_##tag] = (1 << GUMBO_NAMESPACE_MATHML)
+
+#define TAGSET_INCLUDES(tagset, namespace, tag) \
+  (tag < GUMBO_TAG_LAST && tagset[(int) tag] == (1 << (int) namespace))
+
+// selected forward declarations as it is getting hard to find
+// an appropriate order
+static bool node_html_tag_is(const GumboNode*, GumboTag);
+static GumboInsertionMode get_current_template_insertion_mode(
+    const GumboParser*);
+static bool handle_in_template(GumboParser*, GumboToken*);
+static void destroy_node(GumboParser*, GumboNode*);
+
+static void* malloc_wrapper(void* unused, size_t size) { return malloc(size); }
+
+static void free_wrapper(void* unused, void* ptr) { free(ptr); }
+
+const GumboOptions kGumboDefaultOptions = {&malloc_wrapper, &free_wrapper, NULL,
+    8, false, -1, GUMBO_TAG_LAST, GUMBO_NAMESPACE_HTML};
+
+static const GumboStringPiece kDoctypeHtml = GUMBO_STRING("html");
+static const GumboStringPiece kPublicIdHtml4_0 =
+    GUMBO_STRING("-//W3C//DTD HTML 4.0//EN");
+static const GumboStringPiece kPublicIdHtml4_01 =
+    GUMBO_STRING("-//W3C//DTD HTML 4.01//EN");
+static const GumboStringPiece kPublicIdXhtml1_0 =
+    GUMBO_STRING("-//W3C//DTD XHTML 1.0 Strict//EN");
+static const GumboStringPiece kPublicIdXhtml1_1 =
+    GUMBO_STRING("-//W3C//DTD XHTML 1.1//EN");
+static const GumboStringPiece kSystemIdRecHtml4_0 =
+    GUMBO_STRING("http://www.w3.org/TR/REC-html40/strict.dtd");
+static const GumboStringPiece kSystemIdHtml4 =
+    GUMBO_STRING("http://www.w3.org/TR/html4/strict.dtd");
+static const GumboStringPiece kSystemIdXhtmlStrict1_1 =
+    GUMBO_STRING("http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd");
+static const GumboStringPiece kSystemIdXhtml1_1 =
+    GUMBO_STRING("http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd");
+static const GumboStringPiece kSystemIdLegacyCompat =
+    GUMBO_STRING("about:legacy-compat");
+
+// The doctype arrays have an explicit terminator because we want to pass them
+// to a helper function, and passing them as a pointer discards sizeof
+// information.  The SVG arrays are used only by one-off functions, and so loops
+// over them use sizeof directly instead of a terminator.
+
+static const GumboStringPiece kQuirksModePublicIdPrefixes[] = {
+    GUMBO_STRING("+//Silmaril//dtd html Pro v0r11 19970101//"),
+    GUMBO_STRING("-//AdvaSoft Ltd//DTD HTML 3.0 asWedit + extensions//"),
+    GUMBO_STRING("-//AS//DTD HTML 3.0 asWedit + extensions//"),
+    GUMBO_STRING("-//IETF//DTD HTML 2.0 Level 1//"),
+    GUMBO_STRING("-//IETF//DTD HTML 2.0 Level 2//"),
+    GUMBO_STRING("-//IETF//DTD HTML 2.0 Strict Level 1//"),
+    GUMBO_STRING("-//IETF//DTD HTML 2.0 Strict Level 2//"),
+    GUMBO_STRING("-//IETF//DTD HTML 2.0 Strict//"),
+    GUMBO_STRING("-//IETF//DTD HTML 2.0//"),
+    GUMBO_STRING("-//IETF//DTD HTML 2.1E//"),
+    GUMBO_STRING("-//IETF//DTD HTML 3.0//"),
+    GUMBO_STRING("-//IETF//DTD HTML 3.2 Final//"),
+    GUMBO_STRING("-//IETF//DTD HTML 3.2//"),
+    GUMBO_STRING("-//IETF//DTD HTML 3//"),
+    GUMBO_STRING("-//IETF//DTD HTML Level 0//"),
+    GUMBO_STRING("-//IETF//DTD HTML Level 1//"),
+    GUMBO_STRING("-//IETF//DTD HTML Level 2//"),
+    GUMBO_STRING("-//IETF//DTD HTML Level 3//"),
+    GUMBO_STRING("-//IETF//DTD HTML Strict Level 0//"),
+    GUMBO_STRING("-//IETF//DTD HTML Strict Level 1//"),
+    GUMBO_STRING("-//IETF//DTD HTML Strict Level 2//"),
+    GUMBO_STRING("-//IETF//DTD HTML Strict Level 3//"),
+    GUMBO_STRING("-//IETF//DTD HTML Strict//"),
+    GUMBO_STRING("-//IETF//DTD HTML//"),
+    GUMBO_STRING("-//Metrius//DTD Metrius Presentational//"),
+    GUMBO_STRING("-//Microsoft//DTD Internet Explorer 2.0 HTML Strict//"),
+    GUMBO_STRING("-//Microsoft//DTD Internet Explorer 2.0 HTML//"),
+    GUMBO_STRING("-//Microsoft//DTD Internet Explorer 2.0 Tables//"),
+    GUMBO_STRING("-//Microsoft//DTD Internet Explorer 3.0 HTML Strict//"),
+    GUMBO_STRING("-//Microsoft//DTD Internet Explorer 3.0 HTML//"),
+    GUMBO_STRING("-//Microsoft//DTD Internet Explorer 3.0 Tables//"),
+    GUMBO_STRING("-//Netscape Comm. Corp.//DTD HTML//"),
+    GUMBO_STRING("-//Netscape Comm. Corp.//DTD Strict HTML//"),
+    GUMBO_STRING("-//O'Reilly and Associates//DTD HTML 2.0//"),
+    GUMBO_STRING("-//O'Reilly and Associates//DTD HTML Extended 1.0//"),
+    GUMBO_STRING("-//O'Reilly and Associates//DTD HTML Extended Relaxed 1.0//"),
+    GUMBO_STRING(
+        "-//SoftQuad Software//DTD HoTMetaL PRO 6.0::19990601::)"
+        "extensions to HTML 4.0//"),
+    GUMBO_STRING(
+        "-//SoftQuad//DTD HoTMetaL PRO 4.0::19971010::"
+        "extensions to HTML 4.0//"),
+    GUMBO_STRING("-//Spyglass//DTD HTML 2.0 Extended//"),
+    GUMBO_STRING("-//SQ//DTD HTML 2.0 HoTMetaL + extensions//"),
+    GUMBO_STRING("-//Sun Microsystems Corp.//DTD HotJava HTML//"),
+    GUMBO_STRING("-//Sun Microsystems Corp.//DTD HotJava Strict HTML//"),
+    GUMBO_STRING("-//W3C//DTD HTML 3 1995-03-24//"),
+    GUMBO_STRING("-//W3C//DTD HTML 3.2 Draft//"),
+    GUMBO_STRING("-//W3C//DTD HTML 3.2 Final//"),
+    GUMBO_STRING("-//W3C//DTD HTML 3.2//"),
+    GUMBO_STRING("-//W3C//DTD HTML 3.2S Draft//"),
+    GUMBO_STRING("-//W3C//DTD HTML 4.0 Frameset//"),
+    GUMBO_STRING("-//W3C//DTD HTML 4.0 Transitional//"),
+    GUMBO_STRING("-//W3C//DTD HTML Experimental 19960712//"),
+    GUMBO_STRING("-//W3C//DTD HTML Experimental 970421//"),
+    GUMBO_STRING("-//W3C//DTD W3 HTML//"),
+    GUMBO_STRING("-//W3O//DTD W3 HTML 3.0//"),
+    GUMBO_STRING("-//WebTechs//DTD Mozilla HTML 2.0//"),
+    GUMBO_STRING("-//WebTechs//DTD Mozilla HTML//"), TERMINATOR};
+
+static const GumboStringPiece kQuirksModePublicIdExactMatches[] = {
+    GUMBO_STRING("-//W3O//DTD W3 HTML Strict 3.0//EN//"),
+    GUMBO_STRING("-/W3C/DTD HTML 4.0 Transitional/EN"), GUMBO_STRING("HTML"),
+    TERMINATOR};
+
+static const GumboStringPiece kQuirksModeSystemIdExactMatches[] = {
+    GUMBO_STRING("http://www.ibm.com/data/dtd/v11/ibmxhtml1-transitional.dtd"),
+    TERMINATOR};
+
+static const GumboStringPiece kLimitedQuirksPublicIdPrefixes[] = {
+    GUMBO_STRING("-//W3C//DTD XHTML 1.0 Frameset//"),
+    GUMBO_STRING("-//W3C//DTD XHTML 1.0 Transitional//"), TERMINATOR};
+
+static const GumboStringPiece kLimitedQuirksRequiresSystemIdPublicIdPrefixes[] =
+    {GUMBO_STRING("-//W3C//DTD HTML 4.01 Frameset//"),
+        GUMBO_STRING("-//W3C//DTD HTML 4.01 Transitional//"), TERMINATOR};
+
+// Indexed by GumboNamespaceEnum; keep in sync with that.
+static const char* kLegalXmlns[] = {"http://www.w3.org/1999/xhtml",
+    "http://www.w3.org/2000/svg", "http://www.w3.org/1998/Math/MathML"};
+
+typedef struct _ReplacementEntry {
+  const GumboStringPiece from;
+  const GumboStringPiece to;
+} ReplacementEntry;
+
+#define REPLACEMENT_ENTRY(from, to) \
+  { GUMBO_STRING(from), GUMBO_STRING(to) }
+
+// Static data for SVG attribute replacements.
+// https://html.spec.whatwg.org/multipage/syntax.html#creating-and-inserting-nodes
+static const ReplacementEntry kSvgAttributeReplacements[] = {
+    REPLACEMENT_ENTRY("attributename", "attributeName"),
+    REPLACEMENT_ENTRY("attributetype", "attributeType"),
+    REPLACEMENT_ENTRY("basefrequency", "baseFrequency"),
+    REPLACEMENT_ENTRY("baseprofile", "baseProfile"),
+    REPLACEMENT_ENTRY("calcmode", "calcMode"),
+    REPLACEMENT_ENTRY("clippathunits", "clipPathUnits"),
+    // REPLACEMENT_ENTRY("contentscripttype", "contentScriptType"),
+    // REPLACEMENT_ENTRY("contentstyletype", "contentStyleType"),
+    REPLACEMENT_ENTRY("diffuseconstant", "diffuseConstant"),
+    REPLACEMENT_ENTRY("edgemode", "edgeMode"),
+    // REPLACEMENT_ENTRY("externalresourcesrequired",
+    // "externalResourcesRequired"),
+    // REPLACEMENT_ENTRY("filterres", "filterRes"),
+    REPLACEMENT_ENTRY("filterunits", "filterUnits"),
+    REPLACEMENT_ENTRY("glyphref", "glyphRef"),
+    REPLACEMENT_ENTRY("gradienttransform", "gradientTransform"),
+    REPLACEMENT_ENTRY("gradientunits", "gradientUnits"),
+    REPLACEMENT_ENTRY("kernelmatrix", "kernelMatrix"),
+    REPLACEMENT_ENTRY("kernelunitlength", "kernelUnitLength"),
+    REPLACEMENT_ENTRY("keypoints", "keyPoints"),
+    REPLACEMENT_ENTRY("keysplines", "keySplines"),
+    REPLACEMENT_ENTRY("keytimes", "keyTimes"),
+    REPLACEMENT_ENTRY("lengthadjust", "lengthAdjust"),
+    REPLACEMENT_ENTRY("limitingconeangle", "limitingConeAngle"),
+    REPLACEMENT_ENTRY("markerheight", "markerHeight"),
+    REPLACEMENT_ENTRY("markerunits", "markerUnits"),
+    REPLACEMENT_ENTRY("markerwidth", "markerWidth"),
+    REPLACEMENT_ENTRY("maskcontentunits", "maskContentUnits"),
+    REPLACEMENT_ENTRY("maskunits", "maskUnits"),
+    REPLACEMENT_ENTRY("numoctaves", "numOctaves"),
+    REPLACEMENT_ENTRY("pathlength", "pathLength"),
+    REPLACEMENT_ENTRY("patterncontentunits", "patternContentUnits"),
+    REPLACEMENT_ENTRY("patterntransform", "patternTransform"),
+    REPLACEMENT_ENTRY("patternunits", "patternUnits"),
+    REPLACEMENT_ENTRY("pointsatx", "pointsAtX"),
+    REPLACEMENT_ENTRY("pointsaty", "pointsAtY"),
+    REPLACEMENT_ENTRY("pointsatz", "pointsAtZ"),
+    REPLACEMENT_ENTRY("preservealpha", "preserveAlpha"),
+    REPLACEMENT_ENTRY("preserveaspectratio", "preserveAspectRatio"),
+    REPLACEMENT_ENTRY("primitiveunits", "primitiveUnits"),
+    REPLACEMENT_ENTRY("refx", "refX"), REPLACEMENT_ENTRY("refy", "refY"),
+    REPLACEMENT_ENTRY("repeatcount", "repeatCount"),
+    REPLACEMENT_ENTRY("repeatdur", "repeatDur"),
+    REPLACEMENT_ENTRY("requiredextensions", "requiredExtensions"),
+    REPLACEMENT_ENTRY("requiredfeatures", "requiredFeatures"),
+    REPLACEMENT_ENTRY("specularconstant", "specularConstant"),
+    REPLACEMENT_ENTRY("specularexponent", "specularExponent"),
+    REPLACEMENT_ENTRY("spreadmethod", "spreadMethod"),
+    REPLACEMENT_ENTRY("startoffset", "startOffset"),
+    REPLACEMENT_ENTRY("stddeviation", "stdDeviation"),
+    REPLACEMENT_ENTRY("stitchtiles", "stitchTiles"),
+    REPLACEMENT_ENTRY("surfacescale", "surfaceScale"),
+    REPLACEMENT_ENTRY("systemlanguage", "systemLanguage"),
+    REPLACEMENT_ENTRY("tablevalues", "tableValues"),
+    REPLACEMENT_ENTRY("targetx", "targetX"),
+    REPLACEMENT_ENTRY("targety", "targetY"),
+    REPLACEMENT_ENTRY("textlength", "textLength"),
+    REPLACEMENT_ENTRY("viewbox", "viewBox"),
+    REPLACEMENT_ENTRY("viewtarget", "viewTarget"),
+    REPLACEMENT_ENTRY("xchannelselector", "xChannelSelector"),
+    REPLACEMENT_ENTRY("ychannelselector", "yChannelSelector"),
+    REPLACEMENT_ENTRY("zoomandpan", "zoomAndPan"),
+};
+
+static const ReplacementEntry kSvgTagReplacements[] = {
+    REPLACEMENT_ENTRY("altglyph", "altGlyph"),
+    REPLACEMENT_ENTRY("altglyphdef", "altGlyphDef"),
+    REPLACEMENT_ENTRY("altglyphitem", "altGlyphItem"),
+    REPLACEMENT_ENTRY("animatecolor", "animateColor"),
+    REPLACEMENT_ENTRY("animatemotion", "animateMotion"),
+    REPLACEMENT_ENTRY("animatetransform", "animateTransform"),
+    REPLACEMENT_ENTRY("clippath", "clipPath"),
+    REPLACEMENT_ENTRY("feblend", "feBlend"),
+    REPLACEMENT_ENTRY("fecolormatrix", "feColorMatrix"),
+    REPLACEMENT_ENTRY("fecomponenttransfer", "feComponentTransfer"),
+    REPLACEMENT_ENTRY("fecomposite", "feComposite"),
+    REPLACEMENT_ENTRY("feconvolvematrix", "feConvolveMatrix"),
+    REPLACEMENT_ENTRY("fediffuselighting", "feDiffuseLighting"),
+    REPLACEMENT_ENTRY("fedisplacementmap", "feDisplacementMap"),
+    REPLACEMENT_ENTRY("fedistantlight", "feDistantLight"),
+    REPLACEMENT_ENTRY("feflood", "feFlood"),
+    REPLACEMENT_ENTRY("fefunca", "feFuncA"),
+    REPLACEMENT_ENTRY("fefuncb", "feFuncB"),
+    REPLACEMENT_ENTRY("fefuncg", "feFuncG"),
+    REPLACEMENT_ENTRY("fefuncr", "feFuncR"),
+    REPLACEMENT_ENTRY("fegaussianblur", "feGaussianBlur"),
+    REPLACEMENT_ENTRY("feimage", "feImage"),
+    REPLACEMENT_ENTRY("femerge", "feMerge"),
+    REPLACEMENT_ENTRY("femergenode", "feMergeNode"),
+    REPLACEMENT_ENTRY("femorphology", "feMorphology"),
+    REPLACEMENT_ENTRY("feoffset", "feOffset"),
+    REPLACEMENT_ENTRY("fepointlight", "fePointLight"),
+    REPLACEMENT_ENTRY("fespecularlighting", "feSpecularLighting"),
+    REPLACEMENT_ENTRY("fespotlight", "feSpotLight"),
+    REPLACEMENT_ENTRY("fetile", "feTile"),
+    REPLACEMENT_ENTRY("feturbulence", "feTurbulence"),
+    REPLACEMENT_ENTRY("foreignobject", "foreignObject"),
+    REPLACEMENT_ENTRY("glyphref", "glyphRef"),
+    REPLACEMENT_ENTRY("lineargradient", "linearGradient"),
+    REPLACEMENT_ENTRY("radialgradient", "radialGradient"),
+    REPLACEMENT_ENTRY("textpath", "textPath"),
+};
+
+typedef struct _NamespacedAttributeReplacement {
+  const char* from;
+  const char* local_name;
+  const GumboAttributeNamespaceEnum attr_namespace;
+} NamespacedAttributeReplacement;
+
+static const NamespacedAttributeReplacement kForeignAttributeReplacements[] = {
+    {"xlink:actuate", "actuate", GUMBO_ATTR_NAMESPACE_XLINK},
+    {"xlink:actuate", "actuate", GUMBO_ATTR_NAMESPACE_XLINK},
+    {"xlink:href", "href", GUMBO_ATTR_NAMESPACE_XLINK},
+    {"xlink:role", "role", GUMBO_ATTR_NAMESPACE_XLINK},
+    {"xlink:show", "show", GUMBO_ATTR_NAMESPACE_XLINK},
+    {"xlink:title", "title", GUMBO_ATTR_NAMESPACE_XLINK},
+    {"xlink:type", "type", GUMBO_ATTR_NAMESPACE_XLINK},
+    {"xml:base", "base", GUMBO_ATTR_NAMESPACE_XML},
+    {"xml:lang", "lang", GUMBO_ATTR_NAMESPACE_XML},
+    {"xml:space", "space", GUMBO_ATTR_NAMESPACE_XML},
+    {"xmlns", "xmlns", GUMBO_ATTR_NAMESPACE_XMLNS},
+    {"xmlns:xlink", "xlink", GUMBO_ATTR_NAMESPACE_XMLNS},
+};
+
+// The "scope marker" for the list of active formatting elements.  We use a
+// pointer to this as a generic marker element, since the particular element
+// scope doesn't matter.
+static const GumboNode kActiveFormattingScopeMarker;
+
+// The tag_is and tag_in function use true & false to denote start & end tags,
+// but for readability, we define constants for them here.
+static const bool kStartTag = true;
+static const bool kEndTag = false;
+
+// Because GumboStringPieces are immutable, we can't insert a character directly
+// into a text node.  Instead, we accumulate all pending characters here and
+// flush them out to a text node whenever a new element is inserted.
+//
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#insert-a-character
+typedef struct _TextNodeBufferState {
+  // The accumulated text to be inserted into the current text node.
+  GumboStringBuffer _buffer;
+
+  // A pointer to the original text represented by this text node.  Note that
+  // because of foster parenting and other strange DOM manipulations, this may
+  // include other non-text HTML tags in it; it is defined as the span of
+  // original text from the first character in this text node to the last
+  // character in this text node.
+  const char* _start_original_text;
+
+  // The source position of the start of this text node.
+  GumboSourcePosition _start_position;
+
+  // The type of node that will be inserted (TEXT, CDATA, or WHITESPACE).
+  GumboNodeType _type;
+} TextNodeBufferState;
+
+typedef struct GumboInternalParserState {
+  // http://www.whatwg.org/specs/web-apps/current-work/complete/parsing.html#insertion-mode
+  GumboInsertionMode _insertion_mode;
+
+  // Used for run_generic_parsing_algorithm, which needs to switch back to the
+  // original insertion mode at its conclusion.
+  GumboInsertionMode _original_insertion_mode;
+
+  // http://www.whatwg.org/specs/web-apps/current-work/complete/parsing.html#the-stack-of-open-elements
+  GumboVector /*GumboNode*/ _open_elements;
+
+  // http://www.whatwg.org/specs/web-apps/current-work/complete/parsing.html#the-list-of-active-formatting-elements
+  GumboVector /*GumboNode*/ _active_formatting_elements;
+
+  // The stack of template insertion modes.
+  // http://www.whatwg.org/specs/web-apps/current-work/multipage/parsing.html#the-insertion-mode
+  GumboVector /*InsertionMode*/ _template_insertion_modes;
+
+  // http://www.whatwg.org/specs/web-apps/current-work/complete/parsing.html#the-element-pointers
+  GumboNode* _head_element;
+  GumboNode* _form_element;
+
+  // The element used as fragment context when parsing in fragment mode
+  GumboNode* _fragment_ctx;
+
+  // The flag for when the spec says "Reprocess the current token in..."
+  bool _reprocess_current_token;
+
+  // The flag for "acknowledge the token's self-closing flag".
+  bool _self_closing_flag_acknowledged;
+
+  // The "frameset-ok" flag from the spec.
+  bool _frameset_ok;
+
+  // The flag for "If the next token is a LINE FEED, ignore that token...".
+  bool _ignore_next_linefeed;
+
+  // The flag for "whenever a node would be inserted into the current node, it
+  // must instead be foster parented".  This is used for misnested table
+  // content, which needs to be handled according to "in body" rules yet foster
+  // parented outside of the table.
+  // It would perhaps be more explicit to have this as a parameter to
+  // handle_in_body and insert_element, but given how special-purpose this is
+  // and the number of call-sites that would need to take the extra parameter,
+  // it's easier just to have a state flag.
+  bool _foster_parent_insertions;
+
+  // The accumulated text node buffer state.
+  TextNodeBufferState _text_node;
+
+  // The current token.
+  GumboToken* _current_token;
+
+  // The way that the spec is written, the </body> and </html> tags are *always*
+  // implicit, because encountering one of those tokens merely switches the
+  // insertion mode out of "in body".  So we have individual state flags for
+  // those end tags that are then inspected by pop_current_node when the <body>
+  // and <html> nodes are popped to set the GUMBO_INSERTION_IMPLICIT_END_TAG
+  // flag appropriately.
+  bool _closed_body_tag;
+  bool _closed_html_tag;
+} GumboParserState;
+
+static bool token_has_attribute(const GumboToken* token, const char* name) {
+  assert(token->type == GUMBO_TOKEN_START_TAG);
+  return gumbo_get_attribute(&token->v.start_tag.attributes, name) != NULL;
+}
+
+// Checks if the value of the specified attribute is a case-insensitive match
+// for the specified string.
+static bool attribute_matches(
+    const GumboVector* attributes, const char* name, const char* value) {
+  const GumboAttribute* attr = gumbo_get_attribute(attributes, name);
+  return attr ? strcasecmp(value, attr->value) == 0 : false;
+}
+
+// Checks if the value of the specified attribute is a case-sensitive match
+// for the specified string.
+static bool attribute_matches_case_sensitive(
+    const GumboVector* attributes, const char* name, const char* value) {
+  const GumboAttribute* attr = gumbo_get_attribute(attributes, name);
+  return attr ? strcmp(value, attr->value) == 0 : false;
+}
+
+// Checks if the specified attribute vectors are identical.
+static bool all_attributes_match(
+    const GumboVector* attr1, const GumboVector* attr2) {
+  unsigned int num_unmatched_attr2_elements = attr2->length;
+  for (unsigned int i = 0; i < attr1->length; ++i) {
+    const GumboAttribute* attr = attr1->data[i];
+    if (attribute_matches_case_sensitive(attr2, attr->name, attr->value)) {
+      --num_unmatched_attr2_elements;
+    } else {
+      return false;
+    }
+  }
+  return num_unmatched_attr2_elements == 0;
+}
+
+static void set_frameset_not_ok(GumboParser* parser) {
+  gumbo_debug("Setting frameset_ok to false.\n");
+  parser->_parser_state->_frameset_ok = false;
+}
+
+static GumboNode* create_node(GumboParser* parser, GumboNodeType type) {
+  GumboNode* node = gumbo_parser_allocate(parser, sizeof(GumboNode));
+  node->parent = NULL;
+  node->index_within_parent = -1;
+  node->type = type;
+  node->parse_flags = GUMBO_INSERTION_NORMAL;
+  return node;
+}
+
+static GumboNode* new_document_node(GumboParser* parser) {
+  GumboNode* document_node = create_node(parser, GUMBO_NODE_DOCUMENT);
+  document_node->parse_flags = GUMBO_INSERTION_BY_PARSER;
+  gumbo_vector_init(parser, 1, &document_node->v.document.children);
+
+  // Must be initialized explicitly, as there's no guarantee that we'll see a
+  // doc type token.
+  GumboDocument* document = &document_node->v.document;
+  document->has_doctype = false;
+  document->name = NULL;
+  document->public_identifier = NULL;
+  document->system_identifier = NULL;
+  return document_node;
+}
+
+static void output_init(GumboParser* parser) {
+  GumboOutput* output = gumbo_parser_allocate(parser, sizeof(GumboOutput));
+  output->root = NULL;
+  output->document = new_document_node(parser);
+  parser->_output = output;
+  gumbo_init_errors(parser);
+}
+
+static void parser_state_init(GumboParser* parser) {
+  GumboParserState* parser_state =
+      gumbo_parser_allocate(parser, sizeof(GumboParserState));
+  parser_state->_insertion_mode = GUMBO_INSERTION_MODE_INITIAL;
+  parser_state->_reprocess_current_token = false;
+  parser_state->_frameset_ok = true;
+  parser_state->_ignore_next_linefeed = false;
+  parser_state->_foster_parent_insertions = false;
+  parser_state->_text_node._type = GUMBO_NODE_WHITESPACE;
+  gumbo_string_buffer_init(parser, &parser_state->_text_node._buffer);
+  gumbo_vector_init(parser, 10, &parser_state->_open_elements);
+  gumbo_vector_init(parser, 5, &parser_state->_active_formatting_elements);
+  gumbo_vector_init(parser, 5, &parser_state->_template_insertion_modes);
+  parser_state->_head_element = NULL;
+  parser_state->_form_element = NULL;
+  parser_state->_fragment_ctx = NULL;
+  parser_state->_current_token = NULL;
+  parser_state->_closed_body_tag = false;
+  parser_state->_closed_html_tag = false;
+  parser->_parser_state = parser_state;
+}
+
+static void parser_state_destroy(GumboParser* parser) {
+  GumboParserState* state = parser->_parser_state;
+  if (state->_fragment_ctx) {
+    destroy_node(parser, state->_fragment_ctx);
+  }
+  gumbo_vector_destroy(parser, &state->_active_formatting_elements);
+  gumbo_vector_destroy(parser, &state->_open_elements);
+  gumbo_vector_destroy(parser, &state->_template_insertion_modes);
+  gumbo_string_buffer_destroy(parser, &state->_text_node._buffer);
+  gumbo_parser_deallocate(parser, state);
+}
+
+static GumboNode* get_document_node(GumboParser* parser) {
+  return parser->_output->document;
+}
+
+static bool is_fragment_parser(const GumboParser* parser) {
+  return !!parser->_parser_state->_fragment_ctx;
+}
+
+// Returns the node at the bottom of the stack of open elements, or NULL if no
+// elements have been added yet.
+static GumboNode* get_current_node(GumboParser* parser) {
+  GumboVector* open_elements = &parser->_parser_state->_open_elements;
+  if (open_elements->length == 0) {
+    assert(!parser->_output->root);
+    return NULL;
+  }
+  assert(open_elements->length > 0);
+  assert(open_elements->data != NULL);
+  return open_elements->data[open_elements->length - 1];
+}
+
+static GumboNode* get_adjusted_current_node(GumboParser* parser) {
+  GumboParserState* state = parser->_parser_state;
+  if (state->_open_elements.length == 1 && state->_fragment_ctx) {
+    return state->_fragment_ctx;
+  }
+  return get_current_node(parser);
+}
+
+// Returns true if the given needle is in the given array of literal
+// GumboStringPieces.  If exact_match is true, this requires that they match
+// exactly; otherwise, this performs a prefix match to check if any of the
+// elements in haystack start with needle.  This always performs a
+// case-insensitive match.
+static bool is_in_static_list(
+    const char* needle, const GumboStringPiece* haystack, bool exact_match) {
+  for (unsigned int i = 0; haystack[i].length > 0; ++i) {
+    if ((exact_match && !strcmp(needle, haystack[i].data)) ||
+        (!exact_match && !strcasecmp(needle, haystack[i].data))) {
+      return true;
+    }
+  }
+  return false;
+}
+
+static void set_insertion_mode(GumboParser* parser, GumboInsertionMode mode) {
+  parser->_parser_state->_insertion_mode = mode;
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/parsing.html#reset-the-insertion-mode-appropriately
+// This is a helper function that returns the appropriate insertion mode instead
+// of setting it.  Returns GUMBO_INSERTION_MODE_INITIAL as a sentinel value to
+// indicate that there is no appropriate insertion mode, and the loop should
+// continue.
+static GumboInsertionMode get_appropriate_insertion_mode(
+    const GumboParser* parser, int index) {
+  const GumboVector* open_elements = &parser->_parser_state->_open_elements;
+  const GumboNode* node = open_elements->data[index];
+  const bool is_last = index == 0;
+
+  if (is_last && is_fragment_parser(parser)) {
+    node = parser->_parser_state->_fragment_ctx;
+  }
+
+  assert(node->type == GUMBO_NODE_ELEMENT || node->type == GUMBO_NODE_TEMPLATE);
+  switch (node->v.element.tag) {
+    case GUMBO_TAG_SELECT: {
+      if (is_last) {
+        return GUMBO_INSERTION_MODE_IN_SELECT;
+      }
+      for (int i = index; i > 0; --i) {
+        const GumboNode* ancestor = open_elements->data[i];
+        if (node_html_tag_is(ancestor, GUMBO_TAG_TEMPLATE)) {
+          return GUMBO_INSERTION_MODE_IN_SELECT;
+        }
+        if (node_html_tag_is(ancestor, GUMBO_TAG_TABLE)) {
+          return GUMBO_INSERTION_MODE_IN_SELECT_IN_TABLE;
+        }
+      }
+      return GUMBO_INSERTION_MODE_IN_SELECT;
+    }
+    case GUMBO_TAG_TD:
+    case GUMBO_TAG_TH:
+      if (!is_last) return GUMBO_INSERTION_MODE_IN_CELL;
+      break;
+    case GUMBO_TAG_TR:
+      return GUMBO_INSERTION_MODE_IN_ROW;
+    case GUMBO_TAG_TBODY:
+    case GUMBO_TAG_THEAD:
+    case GUMBO_TAG_TFOOT:
+      return GUMBO_INSERTION_MODE_IN_TABLE_BODY;
+    case GUMBO_TAG_CAPTION:
+      return GUMBO_INSERTION_MODE_IN_CAPTION;
+    case GUMBO_TAG_COLGROUP:
+      return GUMBO_INSERTION_MODE_IN_COLUMN_GROUP;
+    case GUMBO_TAG_TABLE:
+      return GUMBO_INSERTION_MODE_IN_TABLE;
+    case GUMBO_TAG_TEMPLATE:
+      return get_current_template_insertion_mode(parser);
+    case GUMBO_TAG_HEAD:
+      if (!is_last) return GUMBO_INSERTION_MODE_IN_HEAD;
+      break;
+    case GUMBO_TAG_BODY:
+      return GUMBO_INSERTION_MODE_IN_BODY;
+    case GUMBO_TAG_FRAMESET:
+      return GUMBO_INSERTION_MODE_IN_FRAMESET;
+    case GUMBO_TAG_HTML:
+      return parser->_parser_state->_head_element
+                 ? GUMBO_INSERTION_MODE_AFTER_HEAD
+                 : GUMBO_INSERTION_MODE_BEFORE_HEAD;
+    default:
+      break;
+  }
+  return is_last ? GUMBO_INSERTION_MODE_IN_BODY : GUMBO_INSERTION_MODE_INITIAL;
+}
+
+// This performs the actual "reset the insertion mode" loop.
+static void reset_insertion_mode_appropriately(GumboParser* parser) {
+  const GumboVector* open_elements = &parser->_parser_state->_open_elements;
+  for (int i = open_elements->length; --i >= 0;) {
+    GumboInsertionMode mode = get_appropriate_insertion_mode(parser, i);
+    if (mode != GUMBO_INSERTION_MODE_INITIAL) {
+      set_insertion_mode(parser, mode);
+      return;
+    }
+  }
+  // Should never get here, because is_last will be set on the last iteration
+  // and will force GUMBO_INSERTION_MODE_IN_BODY.
+  assert(0);
+}
+
+static GumboError* parser_add_parse_error(
+    GumboParser* parser, const GumboToken* token) {
+  gumbo_debug("Adding parse error.\n");
+  GumboError* error = gumbo_add_error(parser);
+  if (!error) {
+    return NULL;
+  }
+  error->type = GUMBO_ERR_PARSER;
+  error->position = token->position;
+  error->original_text = token->original_text.data;
+  GumboParserError* extra_data = &error->v.parser;
+  extra_data->input_type = token->type;
+  extra_data->input_tag = GUMBO_TAG_UNKNOWN;
+  if (token->type == GUMBO_TOKEN_START_TAG) {
+    extra_data->input_tag = token->v.start_tag.tag;
+  } else if (token->type == GUMBO_TOKEN_END_TAG) {
+    extra_data->input_tag = token->v.end_tag;
+  }
+  GumboParserState* state = parser->_parser_state;
+  extra_data->parser_state = state->_insertion_mode;
+  gumbo_vector_init(
+      parser, state->_open_elements.length, &extra_data->tag_stack);
+  for (unsigned int i = 0; i < state->_open_elements.length; ++i) {
+    const GumboNode* node = state->_open_elements.data[i];
+    assert(
+        node->type == GUMBO_NODE_ELEMENT || node->type == GUMBO_NODE_TEMPLATE);
+    gumbo_vector_add(
+        parser, (void*) node->v.element.tag, &extra_data->tag_stack);
+  }
+  return error;
+}
+
+// Returns true if the specified token is either a start or end tag (specified
+// by is_start) with one of the tag types in the varargs list.  Terminate the
+// list with GUMBO_TAG_LAST; this functions as a sentinel since no portion of
+// the spec references tags that are not in the spec.
+static bool tag_in(
+    const GumboToken* token, bool is_start, const gumbo_tagset tags) {
+  GumboTag token_tag;
+  if (is_start && token->type == GUMBO_TOKEN_START_TAG) {
+    token_tag = token->v.start_tag.tag;
+  } else if (!is_start && token->type == GUMBO_TOKEN_END_TAG) {
+    token_tag = token->v.end_tag;
+  } else {
+    return false;
+  }
+  return (token_tag < GUMBO_TAG_LAST && tags[(int) token_tag] != 0);
+}
+
+// Like tag_in, but for the single-tag case.
+static bool tag_is(const GumboToken* token, bool is_start, GumboTag tag) {
+  if (is_start && token->type == GUMBO_TOKEN_START_TAG) {
+    return token->v.start_tag.tag == tag;
+  } else if (!is_start && token->type == GUMBO_TOKEN_END_TAG) {
+    return token->v.end_tag == tag;
+  } else {
+    return false;
+  }
+}
+
+// Like tag_in, but checks for the tag of a node, rather than a token.
+static bool node_tag_in_set(const GumboNode* node, const gumbo_tagset tags) {
+  assert(node != NULL);
+  if (node->type != GUMBO_NODE_ELEMENT && node->type != GUMBO_NODE_TEMPLATE) {
+    return false;
+  }
+  return TAGSET_INCLUDES(
+      tags, node->v.element.tag_namespace, node->v.element.tag);
+}
+
+// Like node_tag_in, but for the single-tag case.
+static bool node_qualified_tag_is(
+    const GumboNode* node, GumboNamespaceEnum ns, GumboTag tag) {
+  assert(node);
+  return (node->type == GUMBO_NODE_ELEMENT ||
+             node->type == GUMBO_NODE_TEMPLATE) &&
+         node->v.element.tag == tag && node->v.element.tag_namespace == ns;
+}
+
+// Like node_tag_in, but for the single-tag case in the HTML namespace
+static bool node_html_tag_is(const GumboNode* node, GumboTag tag) {
+  return node_qualified_tag_is(node, GUMBO_NAMESPACE_HTML, tag);
+}
+
+static void push_template_insertion_mode(
+    GumboParser* parser, GumboInsertionMode mode) {
+  gumbo_vector_add(
+      parser, (void*) mode, &parser->_parser_state->_template_insertion_modes);
+}
+
+static void pop_template_insertion_mode(GumboParser* parser) {
+  gumbo_vector_pop(parser, &parser->_parser_state->_template_insertion_modes);
+}
+
+// Returns the current template insertion mode.  If the stack of template
+// insertion modes is empty, this returns GUMBO_INSERTION_MODE_INITIAL.
+static GumboInsertionMode get_current_template_insertion_mode(
+    const GumboParser* parser) {
+  GumboVector* template_insertion_modes =
+      &parser->_parser_state->_template_insertion_modes;
+  if (template_insertion_modes->length == 0) {
+    return GUMBO_INSERTION_MODE_INITIAL;
+  }
+  return (GumboInsertionMode)
+      (intptr_t) template_insertion_modes->data[(template_insertion_modes->length - 1)];
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/multipage/tree-construction.html#mathml-text-integration-point
+static bool is_mathml_integration_point(const GumboNode* node) {
+  return node_tag_in_set(
+      node, (gumbo_tagset){TAG_MATHML(MI), TAG_MATHML(MO), TAG_MATHML(MN),
+                TAG_MATHML(MS), TAG_MATHML(MTEXT)});
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/multipage/tree-construction.html#html-integration-point
+static bool is_html_integration_point(const GumboNode* node) {
+  return node_tag_in_set(node, (gumbo_tagset){TAG_SVG(FOREIGNOBJECT),
+                                   TAG_SVG(DESC), TAG_SVG(TITLE)}) ||
+         (node_qualified_tag_is(
+              node, GUMBO_NAMESPACE_MATHML, GUMBO_TAG_ANNOTATION_XML) &&
+             (attribute_matches(
+                  &node->v.element.attributes, "encoding", "text/html") ||
+                 attribute_matches(&node->v.element.attributes, "encoding",
+                     "application/xhtml+xml")));
+}
+
+// This represents a place to insert a node, consisting of a target parent and a
+// child index within that parent.  If the node should be inserted at the end of
+// the parent's child, index will be -1.
+typedef struct {
+  GumboNode* target;
+  int index;
+} InsertionLocation;
+
+InsertionLocation get_appropriate_insertion_location(
+    GumboParser* parser, GumboNode* override_target) {
+  InsertionLocation retval = {override_target, -1};
+  if (retval.target == NULL) {
+    // No override target; default to the current node, but special-case the
+    // root node since get_current_node() assumes the stack of open elements is
+    // non-empty.
+    retval.target = parser->_output->root != NULL ? get_current_node(parser)
+                                                  : get_document_node(parser);
+  }
+  if (!parser->_parser_state->_foster_parent_insertions ||
+      !node_tag_in_set(retval.target, (gumbo_tagset){TAG(TABLE), TAG(TBODY),
+                                          TAG(TFOOT), TAG(THEAD), TAG(TR)})) {
+    return retval;
+  }
+
+  // Foster-parenting case.
+  int last_template_index = -1;
+  int last_table_index = -1;
+  GumboVector* open_elements = &parser->_parser_state->_open_elements;
+  for (unsigned int i = 0; i < open_elements->length; ++i) {
+    if (node_html_tag_is(open_elements->data[i], GUMBO_TAG_TEMPLATE)) {
+      last_template_index = i;
+    }
+    if (node_html_tag_is(open_elements->data[i], GUMBO_TAG_TABLE)) {
+      last_table_index = i;
+    }
+  }
+  if (last_template_index != -1 &&
+      (last_table_index == -1 || last_template_index > last_table_index)) {
+    retval.target = open_elements->data[last_template_index];
+    return retval;
+  }
+  if (last_table_index == -1) {
+    retval.target = open_elements->data[0];
+    return retval;
+  }
+  GumboNode* last_table = open_elements->data[last_table_index];
+  if (last_table->parent != NULL) {
+    retval.target = last_table->parent;
+    retval.index = last_table->index_within_parent;
+    return retval;
+  }
+
+  retval.target = open_elements->data[last_table_index - 1];
+  return retval;
+}
+
+// Appends a node to the end of its parent, setting the "parent" and
+// "index_within_parent" fields appropriately.
+static void append_node(
+    GumboParser* parser, GumboNode* parent, GumboNode* node) {
+  assert(node->parent == NULL);
+  assert(node->index_within_parent == -1);
+  GumboVector* children;
+  if (parent->type == GUMBO_NODE_ELEMENT ||
+      parent->type == GUMBO_NODE_TEMPLATE) {
+    children = &parent->v.element.children;
+  } else {
+    assert(parent->type == GUMBO_NODE_DOCUMENT);
+    children = &parent->v.document.children;
+  }
+  node->parent = parent;
+  node->index_within_parent = children->length;
+  gumbo_vector_add(parser, (void*) node, children);
+  assert(node->index_within_parent < children->length);
+}
+
+// Inserts a node at the specified InsertionLocation, updating the
+// "parent" and "index_within_parent" fields of it and all its siblings.
+// If the index of the location is -1, this calls append_node.
+static void insert_node(
+    GumboParser* parser, GumboNode* node, InsertionLocation location) {
+  assert(node->parent == NULL);
+  assert(node->index_within_parent == -1);
+  GumboNode* parent = location.target;
+  int index = location.index;
+  if (index != -1) {
+    GumboVector* children = NULL;
+    if (parent->type == GUMBO_NODE_ELEMENT ||
+        parent->type == GUMBO_NODE_TEMPLATE) {
+      children = &parent->v.element.children;
+    } else if (parent->type == GUMBO_NODE_DOCUMENT) {
+      children = &parent->v.document.children;
+      assert(children->length == 0);
+    } else {
+      assert(0);
+    }
+
+    assert(index >= 0);
+    assert((unsigned int) index < children->length);
+    node->parent = parent;
+    node->index_within_parent = index;
+    gumbo_vector_insert_at(parser, (void*) node, index, children);
+    assert(node->index_within_parent < children->length);
+    for (unsigned int i = index + 1; i < children->length; ++i) {
+      GumboNode* sibling = children->data[i];
+      sibling->index_within_parent = i;
+      assert(sibling->index_within_parent < children->length);
+    }
+  } else {
+    append_node(parser, parent, node);
+  }
+}
+
+static void maybe_flush_text_node_buffer(GumboParser* parser) {
+  GumboParserState* state = parser->_parser_state;
+  TextNodeBufferState* buffer_state = &state->_text_node;
+  if (buffer_state->_buffer.length == 0) {
+    return;
+  }
+
+  assert(buffer_state->_type == GUMBO_NODE_WHITESPACE ||
+         buffer_state->_type == GUMBO_NODE_TEXT ||
+         buffer_state->_type == GUMBO_NODE_CDATA);
+  GumboNode* text_node = create_node(parser, buffer_state->_type);
+  GumboText* text_node_data = &text_node->v.text;
+  text_node_data->text =
+      gumbo_string_buffer_to_string(parser, &buffer_state->_buffer);
+  text_node_data->original_text.data = buffer_state->_start_original_text;
+  text_node_data->original_text.length =
+      state->_current_token->original_text.data -
+      buffer_state->_start_original_text;
+  text_node_data->start_pos = buffer_state->_start_position;
+
+  gumbo_debug("Flushing text node buffer of %.*s.\n",
+      (int) buffer_state->_buffer.length, buffer_state->_buffer.data);
+
+  InsertionLocation location = get_appropriate_insertion_location(parser, NULL);
+  if (location.target->type == GUMBO_NODE_DOCUMENT) {
+    // The DOM does not allow Document nodes to have Text children, so per the
+    // spec, they are dropped on the floor.
+    destroy_node(parser, text_node);
+  } else {
+    insert_node(parser, text_node, location);
+  }
+
+  gumbo_string_buffer_clear(parser, &buffer_state->_buffer);
+  buffer_state->_type = GUMBO_NODE_WHITESPACE;
+  assert(buffer_state->_buffer.length == 0);
+}
+
+static void record_end_of_element(
+    GumboToken* current_token, GumboElement* element) {
+  element->end_pos = current_token->position;
+  element->original_end_tag = current_token->type == GUMBO_TOKEN_END_TAG
+                                  ? current_token->original_text
+                                  : kGumboEmptyString;
+}
+
+static GumboNode* pop_current_node(GumboParser* parser) {
+  GumboParserState* state = parser->_parser_state;
+  maybe_flush_text_node_buffer(parser);
+  if (state->_open_elements.length > 0) {
+    assert(node_html_tag_is(state->_open_elements.data[0], GUMBO_TAG_HTML));
+    gumbo_debug("Popping %s node.\n",
+        gumbo_normalized_tagname(get_current_node(parser)->v.element.tag));
+  }
+  GumboNode* current_node = gumbo_vector_pop(parser, &state->_open_elements);
+  if (!current_node) {
+    assert(state->_open_elements.length == 0);
+    return NULL;
+  }
+  assert(current_node->type == GUMBO_NODE_ELEMENT ||
+         current_node->type == GUMBO_NODE_TEMPLATE);
+  bool is_closed_body_or_html_tag =
+      (node_html_tag_is(current_node, GUMBO_TAG_BODY) &&
+          state->_closed_body_tag) ||
+      (node_html_tag_is(current_node, GUMBO_TAG_HTML) &&
+          state->_closed_html_tag);
+  if ((state->_current_token->type != GUMBO_TOKEN_END_TAG ||
+          !node_html_tag_is(current_node, state->_current_token->v.end_tag)) &&
+      !is_closed_body_or_html_tag) {
+    current_node->parse_flags |= GUMBO_INSERTION_IMPLICIT_END_TAG;
+  }
+  if (!is_closed_body_or_html_tag) {
+    record_end_of_element(state->_current_token, &current_node->v.element);
+  }
+  return current_node;
+}
+
+static void append_comment_node(
+    GumboParser* parser, GumboNode* node, const GumboToken* token) {
+  maybe_flush_text_node_buffer(parser);
+  GumboNode* comment = create_node(parser, GUMBO_NODE_COMMENT);
+  comment->type = GUMBO_NODE_COMMENT;
+  comment->parse_flags = GUMBO_INSERTION_NORMAL;
+  comment->v.text.text = token->v.text;
+  comment->v.text.original_text = token->original_text;
+  comment->v.text.start_pos = token->position;
+  append_node(parser, node, comment);
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#clear-the-stack-back-to-a-table-row-context
+static void clear_stack_to_table_row_context(GumboParser* parser) {
+  while (!node_tag_in_set(get_current_node(parser),
+             (gumbo_tagset){TAG(HTML), TAG(TR), TAG(TEMPLATE)})) {
+    pop_current_node(parser);
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#clear-the-stack-back-to-a-table-context
+static void clear_stack_to_table_context(GumboParser* parser) {
+  while (!node_tag_in_set(get_current_node(parser),
+             (gumbo_tagset){TAG(HTML), TAG(TABLE), TAG(TEMPLATE)})) {
+    pop_current_node(parser);
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#clear-the-stack-back-to-a-table-body-context
+void clear_stack_to_table_body_context(GumboParser* parser) {
+  while (!node_tag_in_set(get_current_node(parser),
+             (gumbo_tagset){TAG(HTML), TAG(TBODY), TAG(TFOOT), TAG(THEAD),
+                 TAG(TEMPLATE)})) {
+    pop_current_node(parser);
+  }
+}
+
+// Creates a parser-inserted element in the HTML namespace and returns it.
+static GumboNode* create_element(GumboParser* parser, GumboTag tag) {
+  GumboNode* node = create_node(parser, GUMBO_NODE_ELEMENT);
+  GumboElement* element = &node->v.element;
+  gumbo_vector_init(parser, 1, &element->children);
+  gumbo_vector_init(parser, 0, &element->attributes);
+  element->tag = tag;
+  element->tag_namespace = GUMBO_NAMESPACE_HTML;
+  element->original_tag = kGumboEmptyString;
+  element->original_end_tag = kGumboEmptyString;
+  element->start_pos = (parser->_parser_state->_current_token)
+                           ? parser->_parser_state->_current_token->position
+                           : kGumboEmptySourcePosition;
+  element->end_pos = kGumboEmptySourcePosition;
+  return node;
+}
+
+// Constructs an element from the given start tag token.
+static GumboNode* create_element_from_token(
+    GumboParser* parser, GumboToken* token, GumboNamespaceEnum tag_namespace) {
+  assert(token->type == GUMBO_TOKEN_START_TAG);
+  GumboTokenStartTag* start_tag = &token->v.start_tag;
+
+  GumboNodeType type = (tag_namespace == GUMBO_NAMESPACE_HTML &&
+                           start_tag->tag == GUMBO_TAG_TEMPLATE)
+                           ? GUMBO_NODE_TEMPLATE
+                           : GUMBO_NODE_ELEMENT;
+
+  GumboNode* node = create_node(parser, type);
+  GumboElement* element = &node->v.element;
+  gumbo_vector_init(parser, 1, &element->children);
+  element->attributes = start_tag->attributes;
+  element->tag = start_tag->tag;
+  element->tag_namespace = tag_namespace;
+
+  assert(token->original_text.length >= 2);
+  assert(token->original_text.data[0] == '<');
+  assert(token->original_text.data[token->original_text.length - 1] == '>');
+  element->original_tag = token->original_text;
+  element->start_pos = token->position;
+  element->original_end_tag = kGumboEmptyString;
+  element->end_pos = kGumboEmptySourcePosition;
+
+  // The element takes ownership of the attributes from the token, so any
+  // allocated-memory fields should be nulled out.
+  start_tag->attributes = kGumboEmptyVector;
+  return node;
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#insert-an-html-element
+static void insert_element(GumboParser* parser, GumboNode* node,
+    bool is_reconstructing_formatting_elements) {
+  GumboParserState* state = parser->_parser_state;
+  // NOTE(jdtang): The text node buffer must always be flushed before inserting
+  // a node, otherwise we're handling nodes in a different order than the spec
+  // mandated.  However, one clause of the spec (character tokens in the body)
+  // requires that we reconstruct the active formatting elements *before* adding
+  // the character, and reconstructing the active formatting elements may itself
+  // result in the insertion of new elements (which should be pushed onto the
+  // stack of open elements before the buffer is flushed).  We solve this (for
+  // the time being, the spec has been rewritten for <template> and the new
+  // version may be simpler here) with a boolean flag to this method.
+  if (!is_reconstructing_formatting_elements) {
+    maybe_flush_text_node_buffer(parser);
+  }
+  InsertionLocation location = get_appropriate_insertion_location(parser, NULL);
+  insert_node(parser, node, location);
+  gumbo_vector_add(parser, (void*) node, &state->_open_elements);
+}
+
+// Convenience method that combines create_element_from_token and
+// insert_element, inserting the generated element directly into the current
+// node.  Returns the node inserted.
+static GumboNode* insert_element_from_token(
+    GumboParser* parser, GumboToken* token) {
+  GumboNode* element =
+      create_element_from_token(parser, token, GUMBO_NAMESPACE_HTML);
+  insert_element(parser, element, false);
+  gumbo_debug("Inserting <%s> element (@%x) from token.\n",
+      gumbo_normalized_tagname(element->v.element.tag), element);
+  return element;
+}
+
+// Convenience method that combines create_element and insert_element, inserting
+// a parser-generated element of a specific tag type.  Returns the node
+// inserted.
+static GumboNode* insert_element_of_tag_type(
+    GumboParser* parser, GumboTag tag, GumboParseFlags reason) {
+  GumboNode* element = create_element(parser, tag);
+  element->parse_flags |= GUMBO_INSERTION_BY_PARSER | reason;
+  insert_element(parser, element, false);
+  gumbo_debug("Inserting %s element (@%x) from tag type.\n",
+      gumbo_normalized_tagname(tag), element);
+  return element;
+}
+
+// Convenience method for creating foreign namespaced element.  Returns the node
+// inserted.
+static GumboNode* insert_foreign_element(
+    GumboParser* parser, GumboToken* token, GumboNamespaceEnum tag_namespace) {
+  assert(token->type == GUMBO_TOKEN_START_TAG);
+  GumboNode* element = create_element_from_token(parser, token, tag_namespace);
+  insert_element(parser, element, false);
+  if (token_has_attribute(token, "xmlns") &&
+      !attribute_matches_case_sensitive(&token->v.start_tag.attributes, "xmlns",
+          kLegalXmlns[tag_namespace])) {
+    // TODO(jdtang): Since there're multiple possible error codes here, we
+    // eventually need reason codes to differentiate them.
+    parser_add_parse_error(parser, token);
+  }
+  if (token_has_attribute(token, "xmlns:xlink") &&
+      !attribute_matches_case_sensitive(&token->v.start_tag.attributes,
+          "xmlns:xlink", "http://www.w3.org/1999/xlink")) {
+    parser_add_parse_error(parser, token);
+  }
+  return element;
+}
+
+static void insert_text_token(GumboParser* parser, GumboToken* token) {
+  assert(token->type == GUMBO_TOKEN_WHITESPACE ||
+         token->type == GUMBO_TOKEN_CHARACTER ||
+         token->type == GUMBO_TOKEN_NULL || token->type == GUMBO_TOKEN_CDATA);
+  TextNodeBufferState* buffer_state = &parser->_parser_state->_text_node;
+  if (buffer_state->_buffer.length == 0) {
+    // Initialize position fields.
+    buffer_state->_start_original_text = token->original_text.data;
+    buffer_state->_start_position = token->position;
+  }
+  gumbo_string_buffer_append_codepoint(
+      parser, token->v.character, &buffer_state->_buffer);
+  if (token->type == GUMBO_TOKEN_CHARACTER) {
+    buffer_state->_type = GUMBO_NODE_TEXT;
+  } else if (token->type == GUMBO_TOKEN_CDATA) {
+    buffer_state->_type = GUMBO_NODE_CDATA;
+  }
+  gumbo_debug("Inserting text token '%c'.\n", token->v.character);
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#generic-rcdata-element-parsing-algorithm
+static void run_generic_parsing_algorithm(
+    GumboParser* parser, GumboToken* token, GumboTokenizerEnum lexer_state) {
+  insert_element_from_token(parser, token);
+  gumbo_tokenizer_set_state(parser, lexer_state);
+  parser->_parser_state->_original_insertion_mode =
+      parser->_parser_state->_insertion_mode;
+  parser->_parser_state->_insertion_mode = GUMBO_INSERTION_MODE_TEXT;
+}
+
+static void acknowledge_self_closing_tag(GumboParser* parser) {
+  parser->_parser_state->_self_closing_flag_acknowledged = true;
+}
+
+// Returns true if there's an anchor tag in the list of active formatting
+// elements, and fills in its index if so.
+static bool find_last_anchor_index(GumboParser* parser, int* anchor_index) {
+  GumboVector* elements = &parser->_parser_state->_active_formatting_elements;
+  for (int i = elements->length; --i >= 0;) {
+    GumboNode* node = elements->data[i];
+    if (node == &kActiveFormattingScopeMarker) {
+      return false;
+    }
+    if (node_html_tag_is(node, GUMBO_TAG_A)) {
+      *anchor_index = i;
+      return true;
+    }
+  }
+  return false;
+}
+
+// Counts the number of open formatting elements in the list of active
+// formatting elements (after the last active scope marker) that have a specific
+// tag.  If this is > 0, then earliest_matching_index will be filled in with the
+// index of the first such element.
+static int count_formatting_elements_of_tag(GumboParser* parser,
+    const GumboNode* desired_node, int* earliest_matching_index) {
+  const GumboElement* desired_element = &desired_node->v.element;
+  GumboVector* elements = &parser->_parser_state->_active_formatting_elements;
+  int num_identical_elements = 0;
+  for (int i = elements->length; --i >= 0;) {
+    GumboNode* node = elements->data[i];
+    if (node == &kActiveFormattingScopeMarker) {
+      break;
+    }
+    assert(node->type == GUMBO_NODE_ELEMENT);
+    if (node_qualified_tag_is(
+            node, desired_element->tag_namespace, desired_element->tag) &&
+        all_attributes_match(
+            &node->v.element.attributes, &desired_element->attributes)) {
+      num_identical_elements++;
+      *earliest_matching_index = i;
+    }
+  }
+  return num_identical_elements;
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/parsing.html#reconstruct-the-active-formatting-elements
+static void add_formatting_element(GumboParser* parser, const GumboNode* node) {
+  assert(node == &kActiveFormattingScopeMarker ||
+         node->type == GUMBO_NODE_ELEMENT);
+  GumboVector* elements = &parser->_parser_state->_active_formatting_elements;
+  if (node == &kActiveFormattingScopeMarker) {
+    gumbo_debug("Adding a scope marker.\n");
+  } else {
+    gumbo_debug("Adding a formatting element.\n");
+  }
+
+  // Hunt for identical elements.
+  int earliest_identical_element = elements->length;
+  int num_identical_elements = count_formatting_elements_of_tag(
+      parser, node, &earliest_identical_element);
+
+  // Noah's Ark clause: if there're at least 3, remove the earliest.
+  if (num_identical_elements >= 3) {
+    gumbo_debug("Noah's ark clause: removing element at %d.\n",
+        earliest_identical_element);
+    gumbo_vector_remove_at(parser, earliest_identical_element, elements);
+  }
+
+  gumbo_vector_add(parser, (void*) node, elements);
+}
+
+static bool is_open_element(GumboParser* parser, const GumboNode* node) {
+  GumboVector* open_elements = &parser->_parser_state->_open_elements;
+  for (unsigned int i = 0; i < open_elements->length; ++i) {
+    if (open_elements->data[i] == node) {
+      return true;
+    }
+  }
+  return false;
+}
+
+// Clones attributes, tags, etc. of a node, but does not copy the content.  The
+// clone shares no structure with the original node: all owned strings and
+// values are fresh copies.
+GumboNode* clone_node(
+    GumboParser* parser, GumboNode* node, GumboParseFlags reason) {
+  assert(node->type == GUMBO_NODE_ELEMENT || node->type == GUMBO_NODE_TEMPLATE);
+  GumboNode* new_node = gumbo_parser_allocate(parser, sizeof(GumboNode));
+  *new_node = *node;
+  new_node->parent = NULL;
+  new_node->index_within_parent = -1;
+  // Clear the GUMBO_INSERTION_IMPLICIT_END_TAG flag, as the cloned node may
+  // have a separate end tag.
+  new_node->parse_flags &= ~GUMBO_INSERTION_IMPLICIT_END_TAG;
+  new_node->parse_flags |= reason | GUMBO_INSERTION_BY_PARSER;
+  GumboElement* element = &new_node->v.element;
+  gumbo_vector_init(parser, 1, &element->children);
+
+  const GumboVector* old_attributes = &node->v.element.attributes;
+  gumbo_vector_init(parser, old_attributes->length, &element->attributes);
+  for (unsigned int i = 0; i < old_attributes->length; ++i) {
+    const GumboAttribute* old_attr = old_attributes->data[i];
+    GumboAttribute* attr =
+        gumbo_parser_allocate(parser, sizeof(GumboAttribute));
+    *attr = *old_attr;
+    attr->name = gumbo_copy_stringz(parser, old_attr->name);
+    attr->value = gumbo_copy_stringz(parser, old_attr->value);
+    gumbo_vector_add(parser, attr, &element->attributes);
+  }
+  return new_node;
+}
+
+// "Reconstruct active formatting elements" part of the spec.
+// This implementation is based on the html5lib translation from the mess of
+// GOTOs in the spec to reasonably structured programming.
+// http://code.google.com/p/html5lib/source/browse/python/html5lib/treebuilders/_base.py
+static void reconstruct_active_formatting_elements(GumboParser* parser) {
+  GumboVector* elements = &parser->_parser_state->_active_formatting_elements;
+  // Step 1
+  if (elements->length == 0) {
+    return;
+  }
+
+  // Step 2 & 3
+  unsigned int i = elements->length - 1;
+  GumboNode* element = elements->data[i];
+  if (element == &kActiveFormattingScopeMarker ||
+      is_open_element(parser, element)) {
+    return;
+  }
+
+  // Step 6
+  do {
+    if (i == 0) {
+      // Step 4
+      i = -1;  // Incremented to 0 below.
+      break;
+    }
+    // Step 5
+    element = elements->data[--i];
+  } while (element != &kActiveFormattingScopeMarker &&
+           !is_open_element(parser, element));
+
+  ++i;
+  gumbo_debug("Reconstructing elements from %d on %s parent.\n", i,
+      gumbo_normalized_tagname(get_current_node(parser)->v.element.tag));
+  for (; i < elements->length; ++i) {
+    // Step 7 & 8.
+    assert(elements->length > 0);
+    assert(i < elements->length);
+    element = elements->data[i];
+    assert(element != &kActiveFormattingScopeMarker);
+    GumboNode* clone = clone_node(
+        parser, element, GUMBO_INSERTION_RECONSTRUCTED_FORMATTING_ELEMENT);
+    // Step 9.
+    InsertionLocation location =
+        get_appropriate_insertion_location(parser, NULL);
+    insert_node(parser, clone, location);
+    gumbo_vector_add(
+        parser, (void*) clone, &parser->_parser_state->_open_elements);
+
+    // Step 10.
+    elements->data[i] = clone;
+    gumbo_debug("Reconstructed %s element at %d.\n",
+        gumbo_normalized_tagname(clone->v.element.tag), i);
+  }
+}
+
+static void clear_active_formatting_elements(GumboParser* parser) {
+  GumboVector* elements = &parser->_parser_state->_active_formatting_elements;
+  int num_elements_cleared = 0;
+  const GumboNode* node;
+  do {
+    node = gumbo_vector_pop(parser, elements);
+    ++num_elements_cleared;
+  } while (node && node != &kActiveFormattingScopeMarker);
+  gumbo_debug("Cleared %d elements from active formatting list.\n",
+      num_elements_cleared);
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#the-initial-insertion-mode
+static GumboQuirksModeEnum compute_quirks_mode(
+    const GumboTokenDocType* doctype) {
+  if (doctype->force_quirks || strcmp(doctype->name, kDoctypeHtml.data) ||
+      is_in_static_list(
+          doctype->public_identifier, kQuirksModePublicIdPrefixes, false) ||
+      is_in_static_list(
+          doctype->public_identifier, kQuirksModePublicIdExactMatches, true) ||
+      is_in_static_list(
+          doctype->system_identifier, kQuirksModeSystemIdExactMatches, true) ||
+      (is_in_static_list(doctype->public_identifier,
+           kLimitedQuirksRequiresSystemIdPublicIdPrefixes, false) &&
+          !doctype->has_system_identifier)) {
+    return GUMBO_DOCTYPE_QUIRKS;
+  } else if (is_in_static_list(doctype->public_identifier,
+                 kLimitedQuirksPublicIdPrefixes, false) ||
+             (is_in_static_list(doctype->public_identifier,
+                  kLimitedQuirksRequiresSystemIdPublicIdPrefixes, false) &&
+                 doctype->has_system_identifier)) {
+    return GUMBO_DOCTYPE_LIMITED_QUIRKS;
+  }
+  return GUMBO_DOCTYPE_NO_QUIRKS;
+}
+
+// The following functions are all defined by the "has an element in __ scope"
+// sections of the HTML5 spec:
+// http://www.whatwg.org/specs/web-apps/current-work/multipage/parsing.html#has-an-element-in-the-specific-scope
+// The basic idea behind them is that they check for an element of the given
+// qualified name, contained within a scope formed by a set of other qualified
+// names.  For example, "has an element in list scope" looks for an element of
+// the given qualified name within the nearest enclosing <ol> or <ul>, along
+// with a bunch of generic element types that serve to "firewall" their content
+// from the rest of the document. Note that because of the way the spec is
+// written,
+// all elements are expected to be in the HTML namespace
+static bool has_an_element_in_specific_scope(GumboParser* parser,
+    int expected_size, const GumboTag* expected, bool negate,
+    const gumbo_tagset tags) {
+  GumboVector* open_elements = &parser->_parser_state->_open_elements;
+  for (int i = open_elements->length; --i >= 0;) {
+    const GumboNode* node = open_elements->data[i];
+    if (node->type != GUMBO_NODE_ELEMENT && node->type != GUMBO_NODE_TEMPLATE)
+      continue;
+
+    GumboTag node_tag = node->v.element.tag;
+    GumboNamespaceEnum node_ns = node->v.element.tag_namespace;
+    for (int j = 0; j < expected_size; ++j) {
+      if (node_tag == expected[j] && node_ns == GUMBO_NAMESPACE_HTML)
+        return true;
+    }
+
+    bool found = TAGSET_INCLUDES(tags, node_ns, node_tag);
+    if (negate != found) return false;
+  }
+  return false;
+}
+
+// Checks for the presence of an open element of the specified tag type.
+static bool has_open_element(GumboParser* parser, GumboTag tag) {
+  return has_an_element_in_specific_scope(
+      parser, 1, &tag, false, (gumbo_tagset){TAG(HTML)});
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/multipage/parsing.html#has-an-element-in-scope
+static bool has_an_element_in_scope(GumboParser* parser, GumboTag tag) {
+  return has_an_element_in_specific_scope(parser, 1, &tag, false,
+      (gumbo_tagset){TAG(APPLET), TAG(CAPTION), TAG(HTML), TAG(TABLE), TAG(TD),
+          TAG(TH), TAG(MARQUEE), TAG(OBJECT), TAG(TEMPLATE), TAG_MATHML(MI),
+          TAG_MATHML(MO), TAG_MATHML(MN), TAG_MATHML(MS), TAG_MATHML(MTEXT),
+          TAG_MATHML(ANNOTATION_XML), TAG_SVG(FOREIGNOBJECT), TAG_SVG(DESC),
+          TAG_SVG(TITLE)});
+}
+
+// Like "has an element in scope", but for the specific case of looking for a
+// unique target node, not for any node with a given tag name.  This duplicates
+// much of the algorithm from has_an_element_in_specific_scope because the
+// predicate is different when checking for an exact node, and it's easier &
+// faster just to duplicate the code for this one case than to try and
+// parameterize it.
+static bool has_node_in_scope(GumboParser* parser, const GumboNode* node) {
+  GumboVector* open_elements = &parser->_parser_state->_open_elements;
+  for (int i = open_elements->length; --i >= 0;) {
+    const GumboNode* current = open_elements->data[i];
+    if (current == node) {
+      return true;
+    }
+    if (current->type != GUMBO_NODE_ELEMENT &&
+        current->type != GUMBO_NODE_TEMPLATE) {
+      continue;
+    }
+    if (node_tag_in_set(current,
+            (gumbo_tagset){TAG(APPLET), TAG(CAPTION), TAG(HTML), TAG(TABLE),
+                TAG(TD), TAG(TH), TAG(MARQUEE), TAG(OBJECT), TAG(TEMPLATE),
+                TAG_MATHML(MI), TAG_MATHML(MO), TAG_MATHML(MN), TAG_MATHML(MS),
+                TAG_MATHML(MTEXT), TAG_MATHML(ANNOTATION_XML),
+                TAG_SVG(FOREIGNOBJECT), TAG_SVG(DESC), TAG_SVG(TITLE)})) {
+      return false;
+    }
+  }
+  assert(false);
+  return false;
+}
+
+// Like has_an_element_in_scope, but restricts the expected qualified name to a
+// range of possible qualified names instead of just a single one.
+static bool has_an_element_in_scope_with_tagname(
+    GumboParser* parser, int expected_len, const GumboTag expected[]) {
+  return has_an_element_in_specific_scope(parser, expected_len, expected, false,
+      (gumbo_tagset){TAG(APPLET), TAG(CAPTION), TAG(HTML), TAG(TABLE), TAG(TD),
+          TAG(TH), TAG(MARQUEE), TAG(OBJECT), TAG(TEMPLATE), TAG_MATHML(MI),
+          TAG_MATHML(MO), TAG_MATHML(MN), TAG_MATHML(MS), TAG_MATHML(MTEXT),
+          TAG_MATHML(ANNOTATION_XML), TAG_SVG(FOREIGNOBJECT), TAG_SVG(DESC),
+          TAG_SVG(TITLE)});
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/multipage/parsing.html#has-an-element-in-list-item-scope
+static bool has_an_element_in_list_scope(GumboParser* parser, GumboTag tag) {
+  return has_an_element_in_specific_scope(parser, 1, &tag, false,
+      (gumbo_tagset){TAG(APPLET), TAG(CAPTION), TAG(HTML), TAG(TABLE), TAG(TD),
+          TAG(TH), TAG(MARQUEE), TAG(OBJECT), TAG(TEMPLATE), TAG_MATHML(MI),
+          TAG_MATHML(MO), TAG_MATHML(MN), TAG_MATHML(MS), TAG_MATHML(MTEXT),
+          TAG_MATHML(ANNOTATION_XML), TAG_SVG(FOREIGNOBJECT), TAG_SVG(DESC),
+          TAG_SVG(TITLE), TAG(OL), TAG(UL)});
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/multipage/parsing.html#has-an-element-in-button-scope
+static bool has_an_element_in_button_scope(GumboParser* parser, GumboTag tag) {
+  return has_an_element_in_specific_scope(parser, 1, &tag, false,
+      (gumbo_tagset){TAG(APPLET), TAG(CAPTION), TAG(HTML), TAG(TABLE), TAG(TD),
+          TAG(TH), TAG(MARQUEE), TAG(OBJECT), TAG(TEMPLATE), TAG_MATHML(MI),
+          TAG_MATHML(MO), TAG_MATHML(MN), TAG_MATHML(MS), TAG_MATHML(MTEXT),
+          TAG_MATHML(ANNOTATION_XML), TAG_SVG(FOREIGNOBJECT), TAG_SVG(DESC),
+          TAG_SVG(TITLE), TAG(BUTTON)});
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/multipage/parsing.html#has-an-element-in-table-scope
+static bool has_an_element_in_table_scope(GumboParser* parser, GumboTag tag) {
+  return has_an_element_in_specific_scope(parser, 1, &tag, false,
+      (gumbo_tagset){TAG(HTML), TAG(TABLE), TAG(TEMPLATE)});
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/multipage/parsing.html#has-an-element-in-select-scope
+static bool has_an_element_in_select_scope(GumboParser* parser, GumboTag tag) {
+  return has_an_element_in_specific_scope(
+      parser, 1, &tag, true, (gumbo_tagset){TAG(OPTGROUP), TAG(OPTION)});
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#generate-implied-end-tags
+// "exception" is the "element to exclude from the process" listed in the spec.
+// Pass GUMBO_TAG_LAST to not exclude any of them.
+static void generate_implied_end_tags(GumboParser* parser, GumboTag exception) {
+  for (; node_tag_in_set(get_current_node(parser),
+             (gumbo_tagset){TAG(DD), TAG(DT), TAG(LI), TAG(OPTION),
+                 TAG(OPTGROUP), TAG(P), TAG(RP), TAG(RB), TAG(RT), TAG(RTC)}) &&
+         !node_html_tag_is(get_current_node(parser), exception);
+       pop_current_node(parser))
+    ;
+}
+
+// This is the "generate all implied end tags thoroughly" clause of the spec.
+// https://html.spec.whatwg.org/multipage/syntax.html#closing-elements-that-have-implied-end-tags
+static void generate_all_implied_end_tags_thoroughly(GumboParser* parser) {
+  for (
+      ; node_tag_in_set(get_current_node(parser),
+          (gumbo_tagset){TAG(CAPTION), TAG(COLGROUP), TAG(DD), TAG(DT), TAG(LI),
+              TAG(OPTION), TAG(OPTGROUP), TAG(P), TAG(RP), TAG(RT), TAG(RTC),
+              TAG(TBODY), TAG(TD), TAG(TFOOT), TAG(TH), TAG(HEAD), TAG(TR)});
+      pop_current_node(parser))
+    ;
+}
+
+// This factors out the clauses relating to "act as if an end tag token with tag
+// name "table" had been seen.  Returns true if there's a table element in table
+// scope which was successfully closed, false if not and the token should be
+// ignored.  Does not add parse errors; callers should handle that.
+static bool close_table(GumboParser* parser) {
+  if (!has_an_element_in_table_scope(parser, GUMBO_TAG_TABLE)) {
+    return false;
+  }
+
+  GumboNode* node = pop_current_node(parser);
+  while (!node_html_tag_is(node, GUMBO_TAG_TABLE)) {
+    node = pop_current_node(parser);
+  }
+  reset_insertion_mode_appropriately(parser);
+  return true;
+}
+
+// This factors out the clauses relating to "act as if an end tag token with tag
+// name `cell_tag` had been seen".
+static bool close_table_cell(
+    GumboParser* parser, const GumboToken* token, GumboTag cell_tag) {
+  bool result = true;
+  generate_implied_end_tags(parser, GUMBO_TAG_LAST);
+  const GumboNode* node = get_current_node(parser);
+  if (!node_html_tag_is(node, cell_tag)) {
+    parser_add_parse_error(parser, token);
+    result = false;
+  }
+  do {
+    node = pop_current_node(parser);
+  } while (!node_html_tag_is(node, cell_tag));
+
+  clear_active_formatting_elements(parser);
+  set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_ROW);
+  return result;
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#close-the-cell
+// This holds the logic to determine whether we should close a <td> or a <th>.
+static bool close_current_cell(GumboParser* parser, const GumboToken* token) {
+  if (has_an_element_in_table_scope(parser, GUMBO_TAG_TD)) {
+    assert(!has_an_element_in_table_scope(parser, GUMBO_TAG_TH));
+    return close_table_cell(parser, token, GUMBO_TAG_TD);
+  } else {
+    assert(has_an_element_in_table_scope(parser, GUMBO_TAG_TH));
+    return close_table_cell(parser, token, GUMBO_TAG_TH);
+  }
+}
+
+// This factors out the "act as if an end tag of tag name 'select' had been
+// seen" clause of the spec, since it's referenced in several places.  It pops
+// all nodes from the stack until the current <select> has been closed, then
+// resets the insertion mode appropriately.
+static void close_current_select(GumboParser* parser) {
+  GumboNode* node = pop_current_node(parser);
+  while (!node_html_tag_is(node, GUMBO_TAG_SELECT)) {
+    node = pop_current_node(parser);
+  }
+  reset_insertion_mode_appropriately(parser);
+}
+
+// The list of nodes in the "special" category:
+// http://www.whatwg.org/specs/web-apps/current-work/complete/parsing.html#special
+static bool is_special_node(const GumboNode* node) {
+  assert(node->type == GUMBO_NODE_ELEMENT || node->type == GUMBO_NODE_TEMPLATE);
+  return node_tag_in_set(node,
+      (gumbo_tagset){TAG(ADDRESS), TAG(APPLET), TAG(AREA), TAG(ARTICLE),
+          TAG(ASIDE), TAG(BASE), TAG(BASEFONT), TAG(BGSOUND), TAG(BLOCKQUOTE),
+          TAG(BODY), TAG(BR), TAG(BUTTON), TAG(CAPTION), TAG(CENTER), TAG(COL),
+          TAG(COLGROUP), TAG(MENUITEM), TAG(DD), TAG(DETAILS), TAG(DIR),
+          TAG(DIV), TAG(DL), TAG(DT), TAG(EMBED), TAG(FIELDSET),
+          TAG(FIGCAPTION), TAG(FIGURE), TAG(FOOTER), TAG(FORM), TAG(FRAME),
+          TAG(FRAMESET), TAG(H1), TAG(H2), TAG(H3), TAG(H4), TAG(H5), TAG(H6),
+          TAG(HEAD), TAG(HEADER), TAG(HGROUP), TAG(HR), TAG(HTML), TAG(IFRAME),
+          TAG(IMG), TAG(INPUT), TAG(ISINDEX), TAG(LI), TAG(LINK), TAG(LISTING),
+          TAG(MARQUEE), TAG(MENU), TAG(META), TAG(NAV), TAG(NOEMBED),
+          TAG(NOFRAMES), TAG(NOSCRIPT), TAG(OBJECT), TAG(OL), TAG(P),
+          TAG(PARAM), TAG(PLAINTEXT), TAG(PRE), TAG(SCRIPT), TAG(SECTION),
+          TAG(SELECT), TAG(STYLE), TAG(SUMMARY), TAG(TABLE), TAG(TBODY),
+          TAG(TD), TAG(TEMPLATE), TAG(TEXTAREA), TAG(TFOOT), TAG(TH),
+          TAG(THEAD), TAG(TITLE), TAG(TR), TAG(UL), TAG(WBR), TAG(XMP),
+
+          TAG_MATHML(MI), TAG_MATHML(MO), TAG_MATHML(MN), TAG_MATHML(MS),
+          TAG_MATHML(MTEXT), TAG_MATHML(ANNOTATION_XML),
+
+          TAG_SVG(FOREIGNOBJECT), TAG_SVG(DESC)});
+}
+
+// Implicitly closes currently open elements until it reaches an element with
+// the
+// specified qualified name.  If the elements closed are in the set handled by
+// generate_implied_end_tags, this is normal operation and this function returns
+// true.  Otherwise, a parse error is recorded and this function returns false.
+static bool implicitly_close_tags(GumboParser* parser, GumboToken* token,
+    GumboNamespaceEnum target_ns, GumboTag target) {
+  bool result = true;
+  generate_implied_end_tags(parser, target);
+  if (!node_qualified_tag_is(get_current_node(parser), target_ns, target)) {
+    parser_add_parse_error(parser, token);
+    while (
+        !node_qualified_tag_is(get_current_node(parser), target_ns, target)) {
+      pop_current_node(parser);
+    }
+    result = false;
+  }
+  assert(node_qualified_tag_is(get_current_node(parser), target_ns, target));
+  pop_current_node(parser);
+  return result;
+}
+
+// If the stack of open elements has a <p> tag in button scope, this acts as if
+// a </p> tag was encountered, implicitly closing tags.  Returns false if a
+// parse error occurs.  This is a convenience function because this particular
+// clause appears several times in the spec.
+static bool maybe_implicitly_close_p_tag(
+    GumboParser* parser, GumboToken* token) {
+  if (has_an_element_in_button_scope(parser, GUMBO_TAG_P)) {
+    return implicitly_close_tags(
+        parser, token, GUMBO_NAMESPACE_HTML, GUMBO_TAG_P);
+  }
+  return true;
+}
+
+// Convenience function to encapsulate the logic for closing <li> or <dd>/<dt>
+// tags.  Pass true to is_li for handling <li> tags, false for <dd> and <dt>.
+static void maybe_implicitly_close_list_tag(
+    GumboParser* parser, GumboToken* token, bool is_li) {
+  GumboParserState* state = parser->_parser_state;
+  state->_frameset_ok = false;
+  for (int i = state->_open_elements.length; --i >= 0;) {
+    const GumboNode* node = state->_open_elements.data[i];
+    bool is_list_tag =
+        is_li ? node_html_tag_is(node, GUMBO_TAG_LI)
+              : node_tag_in_set(node, (gumbo_tagset){TAG(DD), TAG(DT)});
+    if (is_list_tag) {
+      implicitly_close_tags(
+          parser, token, node->v.element.tag_namespace, node->v.element.tag);
+      return;
+    }
+    if (is_special_node(node) &&
+        !node_tag_in_set(
+            node, (gumbo_tagset){TAG(ADDRESS), TAG(DIV), TAG(P)})) {
+      return;
+    }
+  }
+}
+
+static void merge_attributes(
+    GumboParser* parser, GumboToken* token, GumboNode* node) {
+  assert(token->type == GUMBO_TOKEN_START_TAG);
+  assert(node->type == GUMBO_NODE_ELEMENT);
+  const GumboVector* token_attr = &token->v.start_tag.attributes;
+  GumboVector* node_attr = &node->v.element.attributes;
+
+  for (unsigned int i = 0; i < token_attr->length; ++i) {
+    GumboAttribute* attr = token_attr->data[i];
+    if (!gumbo_get_attribute(node_attr, attr->name)) {
+      // Ownership of the attribute is transferred by this gumbo_vector_add,
+      // so it has to be nulled out of the original token so it doesn't get
+      // double-deleted.
+      gumbo_vector_add(parser, attr, node_attr);
+      token_attr->data[i] = NULL;
+    }
+  }
+  // When attributes are merged, it means the token has been ignored and merged
+  // with another token, so we need to free its memory.  The attributes that are
+  // transferred need to be nulled-out in the vector above so that they aren't
+  // double-deleted.
+  gumbo_token_destroy(parser, token);
+
+#ifndef NDEBUG
+  // Mark this sentinel so the assertion in the main loop knows it's been
+  // destroyed.
+  token->v.start_tag.attributes = kGumboEmptyVector;
+#endif
+}
+
+const char* gumbo_normalize_svg_tagname(const GumboStringPiece* tag) {
+  for (size_t i = 0; i < sizeof(kSvgTagReplacements) / sizeof(ReplacementEntry);
+       ++i) {
+    const ReplacementEntry* entry = &kSvgTagReplacements[i];
+    if (gumbo_string_equals_ignore_case(tag, &entry->from)) {
+      return entry->to.data;
+    }
+  }
+  return NULL;
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/multipage/tree-construction.html#adjust-foreign-attributes
+// This destructively modifies any matching attributes on the token and sets the
+// namespace appropriately.
+static void adjust_foreign_attributes(GumboParser* parser, GumboToken* token) {
+  assert(token->type == GUMBO_TOKEN_START_TAG);
+  const GumboVector* attributes = &token->v.start_tag.attributes;
+  for (size_t i = 0; i < sizeof(kForeignAttributeReplacements) /
+                             sizeof(NamespacedAttributeReplacement);
+       ++i) {
+    const NamespacedAttributeReplacement* entry =
+        &kForeignAttributeReplacements[i];
+    GumboAttribute* attr = gumbo_get_attribute(attributes, entry->from);
+    if (!attr) {
+      continue;
+    }
+    gumbo_parser_deallocate(parser, (void*) attr->name);
+    attr->attr_namespace = entry->attr_namespace;
+    attr->name = gumbo_copy_stringz(parser, entry->local_name);
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#adjust-svg-attributes
+// This destructively modifies any matching attributes on the token.
+static void adjust_svg_attributes(GumboParser* parser, GumboToken* token) {
+  assert(token->type == GUMBO_TOKEN_START_TAG);
+  const GumboVector* attributes = &token->v.start_tag.attributes;
+  for (size_t i = 0;
+       i < sizeof(kSvgAttributeReplacements) / sizeof(ReplacementEntry); ++i) {
+    const ReplacementEntry* entry = &kSvgAttributeReplacements[i];
+    GumboAttribute* attr = gumbo_get_attribute(attributes, entry->from.data);
+    if (!attr) {
+      continue;
+    }
+    gumbo_parser_deallocate(parser, (void*) attr->name);
+    attr->name = gumbo_copy_stringz(parser, entry->to.data);
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#adjust-mathml-attributes
+// Note that this may destructively modify the token with the new attribute
+// value.
+static void adjust_mathml_attributes(GumboParser* parser, GumboToken* token) {
+  assert(token->type == GUMBO_TOKEN_START_TAG);
+  GumboAttribute* attr =
+      gumbo_get_attribute(&token->v.start_tag.attributes, "definitionurl");
+  if (!attr) {
+    return;
+  }
+  gumbo_parser_deallocate(parser, (void*) attr->name);
+  attr->name = gumbo_copy_stringz(parser, "definitionURL");
+}
+
+static bool doctype_matches(const GumboTokenDocType* doctype,
+    const GumboStringPiece* public_id, const GumboStringPiece* system_id,
+    bool allow_missing_system_id) {
+  return !strcmp(doctype->public_identifier, public_id->data) &&
+         (allow_missing_system_id || doctype->has_system_identifier) &&
+         !strcmp(doctype->system_identifier, system_id->data);
+}
+
+static bool maybe_add_doctype_error(
+    GumboParser* parser, const GumboToken* token) {
+  const GumboTokenDocType* doctype = &token->v.doc_type;
+  bool html_doctype = !strcmp(doctype->name, kDoctypeHtml.data);
+  if ((!html_doctype || doctype->has_public_identifier ||
+          (doctype->has_system_identifier &&
+              !strcmp(
+                  doctype->system_identifier, kSystemIdLegacyCompat.data))) &&
+      !(html_doctype && (doctype_matches(doctype, &kPublicIdHtml4_0,
+                             &kSystemIdRecHtml4_0, true) ||
+                            doctype_matches(doctype, &kPublicIdHtml4_01,
+                                &kSystemIdHtml4, true) ||
+                            doctype_matches(doctype, &kPublicIdXhtml1_0,
+                                &kSystemIdXhtmlStrict1_1, false) ||
+                            doctype_matches(doctype, &kPublicIdXhtml1_1,
+                                &kSystemIdXhtml1_1, false)))) {
+    parser_add_parse_error(parser, token);
+    return false;
+  }
+  return true;
+}
+
+static void remove_from_parent(GumboParser* parser, GumboNode* node) {
+  if (!node->parent) {
+    // The node may not have a parent if, for example, it is a newly-cloned copy
+    // of an active formatting element.  DOM manipulations continue with the
+    // orphaned fragment of the DOM tree until it's appended/foster-parented to
+    // the common ancestor at the end of the adoption agency algorithm.
+    return;
+  }
+  assert(node->parent->type == GUMBO_NODE_ELEMENT);
+  GumboVector* children = &node->parent->v.element.children;
+  int index = gumbo_vector_index_of(children, node);
+  assert(index != -1);
+
+  gumbo_vector_remove_at(parser, index, children);
+  node->parent = NULL;
+  node->index_within_parent = -1;
+  for (unsigned int i = index; i < children->length; ++i) {
+    GumboNode* child = children->data[i];
+    child->index_within_parent = i;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/multipage/the-end.html#an-introduction-to-error-handling-and-strange-cases-in-the-parser
+// Also described in the "in body" handling for end formatting tags.
+static bool adoption_agency_algorithm(
+    GumboParser* parser, GumboToken* token, GumboTag subject) {
+  GumboParserState* state = parser->_parser_state;
+  gumbo_debug("Entering adoption agency algorithm.\n");
+  // Step 1.
+  GumboNode* current_node = get_current_node(parser);
+  if (current_node->v.element.tag_namespace == GUMBO_NAMESPACE_HTML &&
+      current_node->v.element.tag == subject &&
+      gumbo_vector_index_of(
+          &state->_active_formatting_elements, current_node) == -1) {
+    pop_current_node(parser);
+    return false;
+  }
+  // Steps 2-4 & 20:
+  for (unsigned int i = 0; i < 8; ++i) {
+    // Step 5.
+    GumboNode* formatting_node = NULL;
+    int formatting_node_in_open_elements = -1;
+    for (int j = state->_active_formatting_elements.length; --j >= 0;) {
+      GumboNode* current_node = state->_active_formatting_elements.data[j];
+      if (current_node == &kActiveFormattingScopeMarker) {
+        gumbo_debug("Broke on scope marker; aborting.\n");
+        // Last scope marker; abort the algorithm.
+        return false;
+      }
+      if (node_html_tag_is(current_node, subject)) {
+        // Found it.
+        formatting_node = current_node;
+        formatting_node_in_open_elements =
+            gumbo_vector_index_of(&state->_open_elements, formatting_node);
+        gumbo_debug("Formatting element of tag %s at %d.\n",
+            gumbo_normalized_tagname(subject),
+            formatting_node_in_open_elements);
+        break;
+      }
+    }
+    if (!formatting_node) {
+      // No matching tag; not a parse error outright, but fall through to the
+      // "any other end tag" clause (which may potentially add a parse error,
+      // but not always).
+      gumbo_debug("No active formatting elements; aborting.\n");
+      return false;
+    }
+
+    // Step 6
+    if (formatting_node_in_open_elements == -1) {
+      gumbo_debug("Formatting node not on stack of open elements.\n");
+      parser_add_parse_error(parser, token);
+      gumbo_vector_remove(
+          parser, formatting_node, &state->_active_formatting_elements);
+      return false;
+    }
+
+    // Step 7
+    if (!has_an_element_in_scope(parser, formatting_node->v.element.tag)) {
+      parser_add_parse_error(parser, token);
+      gumbo_debug("Element not in scope.\n");
+      return false;
+    }
+
+    // Step 8
+    if (formatting_node != get_current_node(parser)) {
+      parser_add_parse_error(parser, token);  // But continue onwards.
+    }
+    assert(formatting_node);
+    assert(!node_html_tag_is(formatting_node, GUMBO_TAG_HTML));
+    assert(!node_html_tag_is(formatting_node, GUMBO_TAG_BODY));
+
+    // Step 9 & 10
+    GumboNode* furthest_block = NULL;
+    for (unsigned int j = formatting_node_in_open_elements;
+         j < state->_open_elements.length; ++j) {
+      assert(j > 0);
+      GumboNode* current = state->_open_elements.data[j];
+      if (is_special_node(current)) {
+        // Step 9.
+        furthest_block = current;
+        break;
+      }
+    }
+    if (!furthest_block) {
+      // Step 10.
+      while (get_current_node(parser) != formatting_node) {
+        pop_current_node(parser);
+      }
+      // And the formatting element itself.
+      pop_current_node(parser);
+      gumbo_vector_remove(
+          parser, formatting_node, &state->_active_formatting_elements);
+      return false;
+    }
+    assert(!node_html_tag_is(furthest_block, GUMBO_TAG_HTML));
+    assert(furthest_block);
+
+    // Step 11.
+    // Elements may be moved and reparented by this algorithm, so
+    // common_ancestor is not necessarily the same as formatting_node->parent.
+    GumboNode* common_ancestor =
+        state->_open_elements.data[gumbo_vector_index_of(&state->_open_elements,
+                                       formatting_node) -
+                                   1];
+    gumbo_debug("Common ancestor tag = %s, furthest block tag = %s.\n",
+        gumbo_normalized_tagname(common_ancestor->v.element.tag),
+        gumbo_normalized_tagname(furthest_block->v.element.tag));
+
+    // Step 12.
+    int bookmark = gumbo_vector_index_of(
+                       &state->_active_formatting_elements, formatting_node) +
+                   1;
+    gumbo_debug("Bookmark at %d.\n", bookmark);
+    // Step 13.
+    GumboNode* node = furthest_block;
+    GumboNode* last_node = furthest_block;
+    // Must be stored explicitly, in case node is removed from the stack of open
+    // elements, to handle step 9.4.
+    int saved_node_index = gumbo_vector_index_of(&state->_open_elements, node);
+    assert(saved_node_index > 0);
+    // Step 13.1.
+    for (int j = 0;;) {
+      // Step 13.2.
+      ++j;
+      // Step 13.3.
+      int node_index = gumbo_vector_index_of(&state->_open_elements, node);
+      gumbo_debug(
+          "Current index: %d, last index: %d.\n", node_index, saved_node_index);
+      if (node_index == -1) {
+        node_index = saved_node_index;
+      }
+      saved_node_index = --node_index;
+      assert(node_index > 0);
+      assert((unsigned int) node_index < state->_open_elements.capacity);
+      node = state->_open_elements.data[node_index];
+      assert(node->parent);
+      if (node == formatting_node) {
+        // Step 13.4.
+        break;
+      }
+      int formatting_index =
+          gumbo_vector_index_of(&state->_active_formatting_elements, node);
+      if (j > 3 && formatting_index != -1) {
+        // Step 13.5.
+        gumbo_debug("Removing formatting element at %d.\n", formatting_index);
+        gumbo_vector_remove_at(
+            parser, formatting_index, &state->_active_formatting_elements);
+        // Removing the element shifts all indices over by one, so we may need
+        // to move the bookmark.
+        if (formatting_index < bookmark) {
+          --bookmark;
+          gumbo_debug("Moving bookmark to %d.\n", bookmark);
+        }
+        continue;
+      }
+      if (formatting_index == -1) {
+        // Step 13.6.
+        gumbo_vector_remove_at(parser, node_index, &state->_open_elements);
+        continue;
+      }
+      // Step 13.7.
+      // "common ancestor as the intended parent" doesn't actually mean insert
+      // it into the common ancestor; that happens below.
+      node = clone_node(parser, node, GUMBO_INSERTION_ADOPTION_AGENCY_CLONED);
+      assert(formatting_index >= 0);
+      state->_active_formatting_elements.data[formatting_index] = node;
+      assert(node_index >= 0);
+      state->_open_elements.data[node_index] = node;
+      // Step 13.8.
+      if (last_node == furthest_block) {
+        bookmark = formatting_index + 1;
+        gumbo_debug("Bookmark moved to %d.\n", bookmark);
+        assert((unsigned int) bookmark <= state->_active_formatting_elements.length);
+      }
+      // Step 13.9.
+      last_node->parse_flags |= GUMBO_INSERTION_ADOPTION_AGENCY_MOVED;
+      remove_from_parent(parser, last_node);
+      append_node(parser, node, last_node);
+      // Step 13.10.
+      last_node = node;
+    }  // Step 13.11.
+
+    // Step 14.
+    gumbo_debug("Removing %s node from parent ",
+        gumbo_normalized_tagname(last_node->v.element.tag));
+    remove_from_parent(parser, last_node);
+    last_node->parse_flags |= GUMBO_INSERTION_ADOPTION_AGENCY_MOVED;
+    InsertionLocation location =
+        get_appropriate_insertion_location(parser, common_ancestor);
+    gumbo_debug("and inserting it into %s.\n",
+        gumbo_normalized_tagname(location.target->v.element.tag));
+    insert_node(parser, last_node, location);
+
+    // Step 15.
+    GumboNode* new_formatting_node = clone_node(
+        parser, formatting_node, GUMBO_INSERTION_ADOPTION_AGENCY_CLONED);
+    formatting_node->parse_flags |= GUMBO_INSERTION_IMPLICIT_END_TAG;
+
+    // Step 16.  Instead of appending nodes one-by-one, we swap the children
+    // vector of furthest_block with the empty children of new_formatting_node,
+    // reducing memory traffic and allocations.  We still have to reset their
+    // parent pointers, though.
+    GumboVector temp = new_formatting_node->v.element.children;
+    new_formatting_node->v.element.children =
+        furthest_block->v.element.children;
+    furthest_block->v.element.children = temp;
+
+    temp = new_formatting_node->v.element.children;
+    for (unsigned int i = 0; i < temp.length; ++i) {
+      GumboNode* child = temp.data[i];
+      child->parent = new_formatting_node;
+    }
+
+    // Step 17.
+    append_node(parser, furthest_block, new_formatting_node);
+
+    // Step 18.
+    // If the formatting node was before the bookmark, it may shift over all
+    // indices after it, so we need to explicitly find the index and possibly
+    // adjust the bookmark.
+    int formatting_node_index = gumbo_vector_index_of(
+        &state->_active_formatting_elements, formatting_node);
+    assert(formatting_node_index != -1);
+    if (formatting_node_index < bookmark) {
+      gumbo_debug(
+          "Formatting node at %d is before bookmark at %d; decrementing.\n",
+          formatting_node_index, bookmark);
+      --bookmark;
+    }
+    gumbo_vector_remove_at(
+        parser, formatting_node_index, &state->_active_formatting_elements);
+    assert(bookmark >= 0);
+    assert((unsigned int) bookmark <= state->_active_formatting_elements.length);
+    gumbo_vector_insert_at(parser, new_formatting_node, bookmark,
+        &state->_active_formatting_elements);
+
+    // Step 19.
+    gumbo_vector_remove(parser, formatting_node, &state->_open_elements);
+    int insert_at =
+        gumbo_vector_index_of(&state->_open_elements, furthest_block) + 1;
+    assert(insert_at >= 0);
+    assert((unsigned int) insert_at <= state->_open_elements.length);
+    gumbo_vector_insert_at(
+        parser, new_formatting_node, insert_at, &state->_open_elements);
+  }  // Step 20.
+  return true;
+}
+
+// This is here to clean up memory when the spec says "Ignore current token."
+static void ignore_token(GumboParser* parser) {
+  GumboToken* token = parser->_parser_state->_current_token;
+  // Ownership of the token's internal buffers are normally transferred to the
+  // element, but if no element is emitted (as happens in non-verbatim-mode
+  // when a token is ignored), we need to free it here to prevent a memory
+  // leak.
+  gumbo_token_destroy(parser, token);
+#ifndef NDEBUG
+  if (token->type == GUMBO_TOKEN_START_TAG) {
+    // Mark this sentinel so the assertion in the main loop knows it's been
+    // destroyed.
+    token->v.start_tag.attributes = kGumboEmptyVector;
+  }
+#endif
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/the-end.html
+static void finish_parsing(GumboParser* parser) {
+  gumbo_debug("Finishing parsing");
+  maybe_flush_text_node_buffer(parser);
+  GumboParserState* state = parser->_parser_state;
+  for (GumboNode* node = pop_current_node(parser); node;
+       node = pop_current_node(parser)) {
+    if ((node_html_tag_is(node, GUMBO_TAG_BODY) && state->_closed_body_tag) ||
+        (node_html_tag_is(node, GUMBO_TAG_HTML) && state->_closed_html_tag)) {
+      continue;
+    }
+    node->parse_flags |= GUMBO_INSERTION_IMPLICIT_END_TAG;
+  }
+  while (pop_current_node(parser))
+    ;  // Pop them all.
+}
+
+static bool handle_initial(GumboParser* parser, GumboToken* token) {
+  GumboDocument* document = &get_document_node(parser)->v.document;
+  if (token->type == GUMBO_TOKEN_WHITESPACE) {
+    ignore_token(parser);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_document_node(parser), token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    document->has_doctype = true;
+    document->name = token->v.doc_type.name;
+    document->public_identifier = token->v.doc_type.public_identifier;
+    document->system_identifier = token->v.doc_type.system_identifier;
+    document->doc_type_quirks_mode = compute_quirks_mode(&token->v.doc_type);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_BEFORE_HTML);
+    return maybe_add_doctype_error(parser, token);
+  }
+  parser_add_parse_error(parser, token);
+  document->doc_type_quirks_mode = GUMBO_DOCTYPE_QUIRKS;
+  set_insertion_mode(parser, GUMBO_INSERTION_MODE_BEFORE_HTML);
+  parser->_parser_state->_reprocess_current_token = true;
+  return true;
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#the-before-html-insertion-mode
+static bool handle_before_html(GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_document_node(parser), token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_WHITESPACE) {
+    ignore_token(parser);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HTML)) {
+    GumboNode* html_node = insert_element_from_token(parser, token);
+    parser->_output->root = html_node;
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_BEFORE_HEAD);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_END_TAG &&
+             !tag_in(token, false,
+                 (gumbo_tagset){TAG(HEAD), TAG(BODY), TAG(HTML), TAG(BR)})) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else {
+    GumboNode* html_node = insert_element_of_tag_type(
+        parser, GUMBO_TAG_HTML, GUMBO_INSERTION_IMPLIED);
+    assert(html_node);
+    parser->_output->root = html_node;
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_BEFORE_HEAD);
+    parser->_parser_state->_reprocess_current_token = true;
+    return true;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#the-before-head-insertion-mode
+static bool handle_before_head(GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_current_node(parser), token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_WHITESPACE) {
+    ignore_token(parser);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HEAD)) {
+    GumboNode* node = insert_element_from_token(parser, token);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_HEAD);
+    parser->_parser_state->_head_element = node;
+    return true;
+  } else if (token->type == GUMBO_TOKEN_END_TAG &&
+             !tag_in(token, false,
+                 (gumbo_tagset){TAG(HEAD), TAG(BODY), TAG(HTML), TAG(BR)})) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else {
+    GumboNode* node = insert_element_of_tag_type(
+        parser, GUMBO_TAG_HEAD, GUMBO_INSERTION_IMPLIED);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_HEAD);
+    parser->_parser_state->_head_element = node;
+    parser->_parser_state->_reprocess_current_token = true;
+    return true;
+  }
+}
+
+// Forward declarations because of mutual dependencies.
+static bool handle_token(GumboParser* parser, GumboToken* token);
+static bool handle_in_body(GumboParser* parser, GumboToken* token);
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-inhead
+static bool handle_in_head(GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_WHITESPACE) {
+    insert_text_token(parser, token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_current_node(parser), token);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HTML)) {
+    return handle_in_body(parser, token);
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(BASE), TAG(BASEFONT), TAG(BGSOUND),
+                     TAG(MENUITEM), TAG(LINK)})) {
+    insert_element_from_token(parser, token);
+    pop_current_node(parser);
+    acknowledge_self_closing_tag(parser);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_META)) {
+    insert_element_from_token(parser, token);
+    pop_current_node(parser);
+    acknowledge_self_closing_tag(parser);
+    // NOTE(jdtang): Gumbo handles only UTF-8, so the encoding clause of the
+    // spec doesn't apply.  If clients want to handle meta-tag re-encoding, they
+    // should specifically look for that string in the document and re-encode it
+    // before passing to Gumbo.
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_TITLE)) {
+    run_generic_parsing_algorithm(parser, token, GUMBO_LEX_RCDATA);
+    return true;
+  } else if (tag_in(
+                 token, kStartTag, (gumbo_tagset){TAG(NOFRAMES), TAG(STYLE)})) {
+    run_generic_parsing_algorithm(parser, token, GUMBO_LEX_RAWTEXT);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_NOSCRIPT)) {
+    insert_element_from_token(parser, token);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_HEAD_NOSCRIPT);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_SCRIPT)) {
+    run_generic_parsing_algorithm(parser, token, GUMBO_LEX_SCRIPT);
+    return true;
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_HEAD)) {
+    GumboNode* head = pop_current_node(parser);
+    AVOID_UNUSED_VARIABLE_WARNING(head);
+    assert(node_html_tag_is(head, GUMBO_TAG_HEAD));
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_AFTER_HEAD);
+    return true;
+  } else if (tag_in(token, kEndTag,
+                 (gumbo_tagset){TAG(BODY), TAG(HTML), TAG(BR)})) {
+    pop_current_node(parser);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_AFTER_HEAD);
+    parser->_parser_state->_reprocess_current_token = true;
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_TEMPLATE)) {
+    insert_element_from_token(parser, token);
+    add_formatting_element(parser, &kActiveFormattingScopeMarker);
+    parser->_parser_state->_frameset_ok = false;
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TEMPLATE);
+    push_template_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TEMPLATE);
+    return true;
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_TEMPLATE)) {
+    if (!has_open_element(parser, GUMBO_TAG_TEMPLATE)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    generate_all_implied_end_tags_thoroughly(parser);
+    bool success = true;
+    if (!node_html_tag_is(get_current_node(parser), GUMBO_TAG_TEMPLATE)) {
+      parser_add_parse_error(parser, token);
+      success = false;
+    }
+    while (!node_html_tag_is(pop_current_node(parser), GUMBO_TAG_TEMPLATE))
+      ;
+    clear_active_formatting_elements(parser);
+    pop_template_insertion_mode(parser);
+    reset_insertion_mode_appropriately(parser);
+    return success;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HEAD) ||
+             (token->type == GUMBO_TOKEN_END_TAG)) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else {
+    pop_current_node(parser);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_AFTER_HEAD);
+    parser->_parser_state->_reprocess_current_token = true;
+    return true;
+  }
+  return true;
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-inheadnoscript
+static bool handle_in_head_noscript(GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    parser_add_parse_error(parser, token);
+    return false;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HTML)) {
+    return handle_in_body(parser, token);
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_NOSCRIPT)) {
+    const GumboNode* node = pop_current_node(parser);
+    assert(node_html_tag_is(node, GUMBO_TAG_NOSCRIPT));
+    AVOID_UNUSED_VARIABLE_WARNING(node);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_HEAD);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_WHITESPACE ||
+             token->type == GUMBO_TOKEN_COMMENT ||
+             tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(BASEFONT), TAG(BGSOUND), TAG(LINK),
+                     TAG(META), TAG(NOFRAMES), TAG(STYLE)})) {
+    return handle_in_head(parser, token);
+  } else if (tag_in(
+                 token, kStartTag, (gumbo_tagset){TAG(HEAD), TAG(NOSCRIPT)}) ||
+             (token->type == GUMBO_TOKEN_END_TAG &&
+                 !tag_is(token, kEndTag, GUMBO_TAG_BR))) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else {
+    parser_add_parse_error(parser, token);
+    const GumboNode* node = pop_current_node(parser);
+    assert(node_html_tag_is(node, GUMBO_TAG_NOSCRIPT));
+    AVOID_UNUSED_VARIABLE_WARNING(node);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_HEAD);
+    parser->_parser_state->_reprocess_current_token = true;
+    return false;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#the-after-head-insertion-mode
+static bool handle_after_head(GumboParser* parser, GumboToken* token) {
+  GumboParserState* state = parser->_parser_state;
+  if (token->type == GUMBO_TOKEN_WHITESPACE) {
+    insert_text_token(parser, token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_current_node(parser), token);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HTML)) {
+    return handle_in_body(parser, token);
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_BODY)) {
+    insert_element_from_token(parser, token);
+    state->_frameset_ok = false;
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_BODY);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_FRAMESET)) {
+    insert_element_from_token(parser, token);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_FRAMESET);
+    return true;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(BASE), TAG(BASEFONT), TAG(BGSOUND),
+                     TAG(LINK), TAG(META), TAG(NOFRAMES), TAG(SCRIPT),
+                     TAG(STYLE), TAG(TEMPLATE), TAG(TITLE)})) {
+    parser_add_parse_error(parser, token);
+    assert(state->_head_element != NULL);
+    // This must be flushed before we push the head element on, as there may be
+    // pending character tokens that should be attached to the root.
+    maybe_flush_text_node_buffer(parser);
+    gumbo_vector_add(parser, state->_head_element, &state->_open_elements);
+    bool result = handle_in_head(parser, token);
+    gumbo_vector_remove(parser, state->_head_element, &state->_open_elements);
+    return result;
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_TEMPLATE)) {
+    return handle_in_head(parser, token);
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HEAD) ||
+             (token->type == GUMBO_TOKEN_END_TAG &&
+                 !tag_in(token, kEndTag,
+                     (gumbo_tagset){TAG(BODY), TAG(HTML), TAG(BR)}))) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else {
+    insert_element_of_tag_type(parser, GUMBO_TAG_BODY, GUMBO_INSERTION_IMPLIED);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_BODY);
+    state->_reprocess_current_token = true;
+    return true;
+  }
+}
+
+static void destroy_node(GumboParser* parser, GumboNode* node) {
+  switch (node->type) {
+    case GUMBO_NODE_DOCUMENT: {
+      GumboDocument* doc = &node->v.document;
+      for (unsigned int i = 0; i < doc->children.length; ++i) {
+        destroy_node(parser, doc->children.data[i]);
+      }
+      gumbo_parser_deallocate(parser, (void*) doc->children.data);
+      gumbo_parser_deallocate(parser, (void*) doc->name);
+      gumbo_parser_deallocate(parser, (void*) doc->public_identifier);
+      gumbo_parser_deallocate(parser, (void*) doc->system_identifier);
+    } break;
+    case GUMBO_NODE_TEMPLATE:
+    case GUMBO_NODE_ELEMENT:
+      for (unsigned int i = 0; i < node->v.element.attributes.length; ++i) {
+        gumbo_destroy_attribute(parser, node->v.element.attributes.data[i]);
+      }
+      gumbo_parser_deallocate(parser, node->v.element.attributes.data);
+      for (unsigned int i = 0; i < node->v.element.children.length; ++i) {
+        destroy_node(parser, node->v.element.children.data[i]);
+      }
+      gumbo_parser_deallocate(parser, node->v.element.children.data);
+      break;
+    case GUMBO_NODE_TEXT:
+    case GUMBO_NODE_CDATA:
+    case GUMBO_NODE_COMMENT:
+    case GUMBO_NODE_WHITESPACE:
+      gumbo_parser_deallocate(parser, (void*) node->v.text.text);
+      break;
+  }
+  gumbo_parser_deallocate(parser, node);
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-inbody
+static bool handle_in_body(GumboParser* parser, GumboToken* token) {
+  GumboParserState* state = parser->_parser_state;
+  assert(state->_open_elements.length > 0);
+  if (token->type == GUMBO_TOKEN_NULL) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_WHITESPACE) {
+    reconstruct_active_formatting_elements(parser);
+    insert_text_token(parser, token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_CHARACTER ||
+             token->type == GUMBO_TOKEN_CDATA) {
+    reconstruct_active_formatting_elements(parser);
+    insert_text_token(parser, token);
+    set_frameset_not_ok(parser);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_current_node(parser), token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HTML)) {
+    parser_add_parse_error(parser, token);
+    if (has_open_element(parser, GUMBO_TAG_TEMPLATE)) {
+      ignore_token(parser);
+      return false;
+    }
+    assert(parser->_output->root != NULL);
+    assert(parser->_output->root->type == GUMBO_NODE_ELEMENT);
+    merge_attributes(parser, token, parser->_output->root);
+    return false;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(BASE), TAG(BASEFONT), TAG(BGSOUND),
+                     TAG(MENUITEM), TAG(LINK), TAG(META), TAG(NOFRAMES),
+                     TAG(SCRIPT), TAG(STYLE), TAG(TEMPLATE), TAG(TITLE)}) ||
+             tag_is(token, kEndTag, GUMBO_TAG_TEMPLATE)) {
+    return handle_in_head(parser, token);
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_BODY)) {
+    parser_add_parse_error(parser, token);
+    if (state->_open_elements.length < 2 ||
+        !node_html_tag_is(state->_open_elements.data[1], GUMBO_TAG_BODY) ||
+        has_open_element(parser, GUMBO_TAG_TEMPLATE)) {
+      ignore_token(parser);
+      return false;
+    }
+    state->_frameset_ok = false;
+    merge_attributes(parser, token, state->_open_elements.data[1]);
+    return false;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_FRAMESET)) {
+    parser_add_parse_error(parser, token);
+    if (state->_open_elements.length < 2 ||
+        !node_html_tag_is(state->_open_elements.data[1], GUMBO_TAG_BODY) ||
+        !state->_frameset_ok) {
+      ignore_token(parser);
+      return false;
+    }
+    // Save the body node for later removal.
+    GumboNode* body_node = state->_open_elements.data[1];
+
+    // Pop all nodes except root HTML element.
+    GumboNode* node;
+    do {
+      node = pop_current_node(parser);
+    } while (node != state->_open_elements.data[1]);
+
+    // Removing & destroying the body node is going to kill any nodes that have
+    // been added to the list of active formatting elements, and so we should
+    // clear it to prevent a use-after-free if the list of active formatting
+    // elements is reconstructed afterwards.  This may happen if whitespace
+    // follows the </frameset>.
+    clear_active_formatting_elements(parser);
+
+    // Remove the body node.  We may want to factor this out into a generic
+    // helper, but right now this is the only code that needs to do this.
+    GumboVector* children = &parser->_output->root->v.element.children;
+    for (unsigned int i = 0; i < children->length; ++i) {
+      if (children->data[i] == body_node) {
+        gumbo_vector_remove_at(parser, i, children);
+        break;
+      }
+    }
+    destroy_node(parser, body_node);
+
+    // Insert the <frameset>, and switch the insertion mode.
+    insert_element_from_token(parser, token);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_FRAMESET);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_EOF) {
+    for (unsigned int i = 0; i < state->_open_elements.length; ++i) {
+      if (!node_tag_in_set(state->_open_elements.data[i],
+              (gumbo_tagset){TAG(DD), TAG(DT), TAG(LI), TAG(P), TAG(TBODY),
+                  TAG(TD), TAG(TFOOT), TAG(TH), TAG(THEAD), TAG(TR), TAG(BODY),
+                  TAG(HTML)})) {
+        parser_add_parse_error(parser, token);
+      }
+    }
+    if (get_current_template_insertion_mode(parser) !=
+        GUMBO_INSERTION_MODE_INITIAL) {
+      return handle_in_template(parser, token);
+    }
+    return true;
+  } else if (tag_in(token, kEndTag, (gumbo_tagset){TAG(BODY), TAG(HTML)})) {
+    if (!has_an_element_in_scope(parser, GUMBO_TAG_BODY)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    bool success = true;
+    for (unsigned int i = 0; i < state->_open_elements.length; ++i) {
+      if (!node_tag_in_set(state->_open_elements.data[i],
+              (gumbo_tagset){TAG(DD), TAG(DT), TAG(LI), TAG(OPTGROUP),
+                  TAG(OPTION), TAG(P), TAG(RB), TAG(RP), TAG(RT), TAG(RTC),
+                  TAG(TBODY), TAG(TD), TAG(TFOOT), TAG(TH), TAG(THEAD), TAG(TR),
+                  TAG(BODY), TAG(HTML)})) {
+        parser_add_parse_error(parser, token);
+        success = false;
+        break;
+      }
+    }
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_AFTER_BODY);
+    if (tag_is(token, kEndTag, GUMBO_TAG_HTML)) {
+      parser->_parser_state->_reprocess_current_token = true;
+    } else {
+      GumboNode* body = state->_open_elements.data[1];
+      assert(node_html_tag_is(body, GUMBO_TAG_BODY));
+      record_end_of_element(state->_current_token, &body->v.element);
+    }
+    return success;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(ADDRESS), TAG(ARTICLE), TAG(ASIDE),
+                     TAG(BLOCKQUOTE), TAG(CENTER), TAG(DETAILS), TAG(DIR),
+                     TAG(DIV), TAG(DL), TAG(FIELDSET), TAG(FIGCAPTION),
+                     TAG(FIGURE), TAG(FOOTER), TAG(HEADER), TAG(HGROUP),
+                     TAG(MENU), TAG(MAIN), TAG(NAV), TAG(OL), TAG(P),
+                     TAG(SECTION), TAG(SUMMARY), TAG(UL)})) {
+    bool result = maybe_implicitly_close_p_tag(parser, token);
+    insert_element_from_token(parser, token);
+    return result;
+  } else if (tag_in(token, kStartTag, (gumbo_tagset){TAG(H1), TAG(H2), TAG(H3),
+                                          TAG(H4), TAG(H5), TAG(H6)})) {
+    bool result = maybe_implicitly_close_p_tag(parser, token);
+    if (node_tag_in_set(
+            get_current_node(parser), (gumbo_tagset){TAG(H1), TAG(H2), TAG(H3),
+                                          TAG(H4), TAG(H5), TAG(H6)})) {
+      parser_add_parse_error(parser, token);
+      pop_current_node(parser);
+      result = false;
+    }
+    insert_element_from_token(parser, token);
+    return result;
+  } else if (tag_in(token, kStartTag, (gumbo_tagset){TAG(PRE), TAG(LISTING)})) {
+    bool result = maybe_implicitly_close_p_tag(parser, token);
+    insert_element_from_token(parser, token);
+    state->_ignore_next_linefeed = true;
+    state->_frameset_ok = false;
+    return result;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_FORM)) {
+    if (state->_form_element != NULL &&
+        !has_open_element(parser, GUMBO_TAG_TEMPLATE)) {
+      gumbo_debug("Ignoring nested form.\n");
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    bool result = maybe_implicitly_close_p_tag(parser, token);
+    GumboNode* form_element = insert_element_from_token(parser, token);
+    if (!has_open_element(parser, GUMBO_TAG_TEMPLATE)) {
+      state->_form_element = form_element;
+    }
+    return result;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_LI)) {
+    maybe_implicitly_close_list_tag(parser, token, true);
+    bool result = maybe_implicitly_close_p_tag(parser, token);
+    insert_element_from_token(parser, token);
+    return result;
+  } else if (tag_in(token, kStartTag, (gumbo_tagset){TAG(DD), TAG(DT)})) {
+    maybe_implicitly_close_list_tag(parser, token, false);
+    bool result = maybe_implicitly_close_p_tag(parser, token);
+    insert_element_from_token(parser, token);
+    return result;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_PLAINTEXT)) {
+    bool result = maybe_implicitly_close_p_tag(parser, token);
+    insert_element_from_token(parser, token);
+    gumbo_tokenizer_set_state(parser, GUMBO_LEX_PLAINTEXT);
+    return result;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_BUTTON)) {
+    if (has_an_element_in_scope(parser, GUMBO_TAG_BUTTON)) {
+      parser_add_parse_error(parser, token);
+      implicitly_close_tags(
+          parser, token, GUMBO_NAMESPACE_HTML, GUMBO_TAG_BUTTON);
+      state->_reprocess_current_token = true;
+      return false;
+    }
+    reconstruct_active_formatting_elements(parser);
+    insert_element_from_token(parser, token);
+    state->_frameset_ok = false;
+    return true;
+  } else if (tag_in(token, kEndTag,
+                 (gumbo_tagset){TAG(ADDRESS), TAG(ARTICLE), TAG(ASIDE),
+                     TAG(BLOCKQUOTE), TAG(BUTTON), TAG(CENTER), TAG(DETAILS),
+                     TAG(DIR), TAG(DIV), TAG(DL), TAG(FIELDSET),
+                     TAG(FIGCAPTION), TAG(FIGURE), TAG(FOOTER), TAG(HEADER),
+                     TAG(HGROUP), TAG(LISTING), TAG(MAIN), TAG(MENU), TAG(NAV),
+                     TAG(OL), TAG(PRE), TAG(SECTION), TAG(SUMMARY), TAG(UL)})) {
+    GumboTag tag = token->v.end_tag;
+    if (!has_an_element_in_scope(parser, tag)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    implicitly_close_tags(
+        parser, token, GUMBO_NAMESPACE_HTML, token->v.end_tag);
+    return true;
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_FORM)) {
+    if (has_open_element(parser, GUMBO_TAG_TEMPLATE)) {
+      if (!has_an_element_in_scope(parser, GUMBO_TAG_FORM)) {
+        parser_add_parse_error(parser, token);
+        ignore_token(parser);
+        return false;
+      }
+      bool success = true;
+      generate_implied_end_tags(parser, GUMBO_TAG_LAST);
+      if (!node_html_tag_is(get_current_node(parser), GUMBO_TAG_FORM)) {
+        parser_add_parse_error(parser, token);
+        return false;
+      }
+      while (!node_html_tag_is(pop_current_node(parser), GUMBO_TAG_FORM))
+        ;
+      return success;
+    } else {
+      bool result = true;
+      const GumboNode* node = state->_form_element;
+      assert(!node || node->type == GUMBO_NODE_ELEMENT);
+      state->_form_element = NULL;
+      if (!node || !has_node_in_scope(parser, node)) {
+        gumbo_debug("Closing an unopened form.\n");
+        parser_add_parse_error(parser, token);
+        ignore_token(parser);
+        return false;
+      }
+      // This differs from implicitly_close_tags because we remove *only* the
+      // <form> element; other nodes are left in scope.
+      generate_implied_end_tags(parser, GUMBO_TAG_LAST);
+      if (get_current_node(parser) != node) {
+        parser_add_parse_error(parser, token);
+        result = false;
+      }
+
+      GumboVector* open_elements = &state->_open_elements;
+      int index = gumbo_vector_index_of(open_elements, node);
+      assert(index >= 0);
+      gumbo_vector_remove_at(parser, index, open_elements);
+      return result;
+    }
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_P)) {
+    if (!has_an_element_in_button_scope(parser, GUMBO_TAG_P)) {
+      parser_add_parse_error(parser, token);
+      // reconstruct_active_formatting_elements(parser);
+      insert_element_of_tag_type(
+          parser, GUMBO_TAG_P, GUMBO_INSERTION_CONVERTED_FROM_END_TAG);
+      state->_reprocess_current_token = true;
+      return false;
+    }
+    return implicitly_close_tags(
+        parser, token, GUMBO_NAMESPACE_HTML, GUMBO_TAG_P);
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_LI)) {
+    if (!has_an_element_in_list_scope(parser, GUMBO_TAG_LI)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    return implicitly_close_tags(
+        parser, token, GUMBO_NAMESPACE_HTML, GUMBO_TAG_LI);
+  } else if (tag_in(token, kEndTag, (gumbo_tagset){TAG(DD), TAG(DT)})) {
+    assert(token->type == GUMBO_TOKEN_END_TAG);
+    GumboTag token_tag = token->v.end_tag;
+    if (!has_an_element_in_scope(parser, token_tag)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    return implicitly_close_tags(
+        parser, token, GUMBO_NAMESPACE_HTML, token_tag);
+  } else if (tag_in(token, kEndTag, (gumbo_tagset){TAG(H1), TAG(H2), TAG(H3),
+                                        TAG(H4), TAG(H5), TAG(H6)})) {
+    if (!has_an_element_in_scope_with_tagname(
+            parser, 6, (GumboTag[]){GUMBO_TAG_H1, GUMBO_TAG_H2, GUMBO_TAG_H3,
+                           GUMBO_TAG_H4, GUMBO_TAG_H5, GUMBO_TAG_H6})) {
+      // No heading open; ignore the token entirely.
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    } else {
+      generate_implied_end_tags(parser, GUMBO_TAG_LAST);
+      const GumboNode* current_node = get_current_node(parser);
+      bool success = node_html_tag_is(current_node, token->v.end_tag);
+      if (!success) {
+        // There're children of the heading currently open; close them below and
+        // record a parse error.
+        // TODO(jdtang): Add a way to distinguish this error case from the one
+        // above.
+        parser_add_parse_error(parser, token);
+      }
+      do {
+        current_node = pop_current_node(parser);
+      } while (!node_tag_in_set(
+                   current_node, (gumbo_tagset){TAG(H1), TAG(H2), TAG(H3),
+                                     TAG(H4), TAG(H5), TAG(H6)}));
+      return success;
+    }
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_A)) {
+    bool success = true;
+    int last_a;
+    int has_matching_a = find_last_anchor_index(parser, &last_a);
+    if (has_matching_a) {
+      assert(has_matching_a == 1);
+      parser_add_parse_error(parser, token);
+      adoption_agency_algorithm(parser, token, GUMBO_TAG_A);
+      // The adoption agency algorithm usually removes all instances of <a>
+      // from the list of active formatting elements, but in case it doesn't,
+      // we're supposed to do this.  (The conditions where it might not are
+      // listed in the spec.)
+      if (find_last_anchor_index(parser, &last_a)) {
+        void* last_element = gumbo_vector_remove_at(
+            parser, last_a, &state->_active_formatting_elements);
+        gumbo_vector_remove(parser, last_element, &state->_open_elements);
+      }
+      success = false;
+    }
+    reconstruct_active_formatting_elements(parser);
+    add_formatting_element(parser, insert_element_from_token(parser, token));
+    return success;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(B), TAG(BIG), TAG(CODE), TAG(EM), TAG(FONT),
+                     TAG(I), TAG(S), TAG(SMALL), TAG(STRIKE), TAG(STRONG),
+                     TAG(TT), TAG(U)})) {
+    reconstruct_active_formatting_elements(parser);
+    add_formatting_element(parser, insert_element_from_token(parser, token));
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_NOBR)) {
+    bool result = true;
+    reconstruct_active_formatting_elements(parser);
+    if (has_an_element_in_scope(parser, GUMBO_TAG_NOBR)) {
+      result = false;
+      parser_add_parse_error(parser, token);
+      adoption_agency_algorithm(parser, token, GUMBO_TAG_NOBR);
+      reconstruct_active_formatting_elements(parser);
+    }
+    insert_element_from_token(parser, token);
+    add_formatting_element(parser, get_current_node(parser));
+    return result;
+  } else if (tag_in(token, kEndTag,
+                 (gumbo_tagset){TAG(A), TAG(B), TAG(BIG), TAG(CODE), TAG(EM),
+                     TAG(FONT), TAG(I), TAG(NOBR), TAG(S), TAG(SMALL),
+                     TAG(STRIKE), TAG(STRONG), TAG(TT), TAG(U)})) {
+    return adoption_agency_algorithm(parser, token, token->v.end_tag);
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(APPLET), TAG(MARQUEE), TAG(OBJECT)})) {
+    reconstruct_active_formatting_elements(parser);
+    insert_element_from_token(parser, token);
+    add_formatting_element(parser, &kActiveFormattingScopeMarker);
+    set_frameset_not_ok(parser);
+    return true;
+  } else if (tag_in(token, kEndTag,
+                 (gumbo_tagset){TAG(APPLET), TAG(MARQUEE), TAG(OBJECT)})) {
+    GumboTag token_tag = token->v.end_tag;
+    if (!has_an_element_in_table_scope(parser, token_tag)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    implicitly_close_tags(parser, token, GUMBO_NAMESPACE_HTML, token_tag);
+    clear_active_formatting_elements(parser);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_TABLE)) {
+    if (get_document_node(parser)->v.document.doc_type_quirks_mode !=
+        GUMBO_DOCTYPE_QUIRKS) {
+      maybe_implicitly_close_p_tag(parser, token);
+    }
+    insert_element_from_token(parser, token);
+    set_frameset_not_ok(parser);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE);
+    return true;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(AREA), TAG(BR), TAG(EMBED), TAG(IMG),
+                     TAG(IMAGE), TAG(KEYGEN), TAG(WBR)})) {
+    bool success = true;
+    if (tag_is(token, kStartTag, GUMBO_TAG_IMAGE)) {
+      success = false;
+      parser_add_parse_error(parser, token);
+      token->v.start_tag.tag = GUMBO_TAG_IMG;
+    }
+    reconstruct_active_formatting_elements(parser);
+    GumboNode* node = insert_element_from_token(parser, token);
+    if (tag_is(token, kStartTag, GUMBO_TAG_IMAGE)) {
+      success = false;
+      parser_add_parse_error(parser, token);
+      node->v.element.tag = GUMBO_TAG_IMG;
+      node->parse_flags |= GUMBO_INSERTION_FROM_IMAGE;
+    }
+    pop_current_node(parser);
+    acknowledge_self_closing_tag(parser);
+    set_frameset_not_ok(parser);
+    return success;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_INPUT)) {
+    if (!attribute_matches(&token->v.start_tag.attributes, "type", "hidden")) {
+      // Must be before the element is inserted, as that takes ownership of the
+      // token's attribute vector.
+      set_frameset_not_ok(parser);
+    }
+    reconstruct_active_formatting_elements(parser);
+    insert_element_from_token(parser, token);
+    pop_current_node(parser);
+    acknowledge_self_closing_tag(parser);
+    return true;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(PARAM), TAG(SOURCE), TAG(TRACK)})) {
+    insert_element_from_token(parser, token);
+    pop_current_node(parser);
+    acknowledge_self_closing_tag(parser);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HR)) {
+    bool result = maybe_implicitly_close_p_tag(parser, token);
+    insert_element_from_token(parser, token);
+    pop_current_node(parser);
+    acknowledge_self_closing_tag(parser);
+    set_frameset_not_ok(parser);
+    return result;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_ISINDEX)) {
+    parser_add_parse_error(parser, token);
+    if (parser->_parser_state->_form_element != NULL &&
+        !has_open_element(parser, GUMBO_TAG_TEMPLATE)) {
+      ignore_token(parser);
+      return false;
+    }
+    acknowledge_self_closing_tag(parser);
+    maybe_implicitly_close_p_tag(parser, token);
+    set_frameset_not_ok(parser);
+
+    GumboVector* token_attrs = &token->v.start_tag.attributes;
+    GumboAttribute* prompt_attr = gumbo_get_attribute(token_attrs, "prompt");
+    GumboAttribute* action_attr = gumbo_get_attribute(token_attrs, "action");
+    GumboAttribute* name_attr = gumbo_get_attribute(token_attrs, "name");
+
+    GumboNode* form = insert_element_of_tag_type(
+        parser, GUMBO_TAG_FORM, GUMBO_INSERTION_FROM_ISINDEX);
+    if (!has_open_element(parser, GUMBO_TAG_TEMPLATE)) {
+      parser->_parser_state->_form_element = form;
+    }
+    if (action_attr) {
+      gumbo_vector_add(parser, action_attr, &form->v.element.attributes);
+    }
+    insert_element_of_tag_type(
+        parser, GUMBO_TAG_HR, GUMBO_INSERTION_FROM_ISINDEX);
+    pop_current_node(parser);  // <hr>
+
+    insert_element_of_tag_type(
+        parser, GUMBO_TAG_LABEL, GUMBO_INSERTION_FROM_ISINDEX);
+    TextNodeBufferState* text_state = &parser->_parser_state->_text_node;
+    text_state->_start_original_text = token->original_text.data;
+    text_state->_start_position = token->position;
+    text_state->_type = GUMBO_NODE_TEXT;
+    if (prompt_attr) {
+      size_t prompt_attr_length = strlen(prompt_attr->value);
+      gumbo_string_buffer_destroy(parser, &text_state->_buffer);
+      text_state->_buffer.data = gumbo_copy_stringz(parser, prompt_attr->value);
+      text_state->_buffer.length = prompt_attr_length;
+      text_state->_buffer.capacity = prompt_attr_length + 1;
+      gumbo_destroy_attribute(parser, prompt_attr);
+    } else {
+      GumboStringPiece prompt_text =
+          GUMBO_STRING("This is a searchable index. Enter search keywords: ");
+      gumbo_string_buffer_append_string(
+          parser, &prompt_text, &text_state->_buffer);
+    }
+
+    GumboNode* input = insert_element_of_tag_type(
+        parser, GUMBO_TAG_INPUT, GUMBO_INSERTION_FROM_ISINDEX);
+    for (unsigned int i = 0; i < token_attrs->length; ++i) {
+      GumboAttribute* attr = token_attrs->data[i];
+      if (attr != prompt_attr && attr != action_attr && attr != name_attr) {
+        gumbo_vector_add(parser, attr, &input->v.element.attributes);
+      }
+      token_attrs->data[i] = NULL;
+    }
+
+    // All attributes have been successfully transferred and nulled out at this
+    // point, so the call to ignore_token will free the memory for it without
+    // touching the attributes.
+    ignore_token(parser);
+
+    // The name attribute, if present, should be destroyed since it's ignored
+    // when copying over.  The action attribute should be kept since it's moved
+    // to the form.
+    if (name_attr) {
+      gumbo_destroy_attribute(parser, name_attr);
+    }
+
+    GumboAttribute* name =
+        gumbo_parser_allocate(parser, sizeof(GumboAttribute));
+    GumboStringPiece name_str = GUMBO_STRING("name");
+    GumboStringPiece isindex_str = GUMBO_STRING("isindex");
+    name->attr_namespace = GUMBO_ATTR_NAMESPACE_NONE;
+    name->name = gumbo_copy_stringz(parser, "name");
+    name->value = gumbo_copy_stringz(parser, "isindex");
+    name->original_name = name_str;
+    name->original_value = isindex_str;
+    name->name_start = kGumboEmptySourcePosition;
+    name->name_end = kGumboEmptySourcePosition;
+    name->value_start = kGumboEmptySourcePosition;
+    name->value_end = kGumboEmptySourcePosition;
+    gumbo_vector_add(parser, name, &input->v.element.attributes);
+
+    pop_current_node(parser);  // <input>
+    pop_current_node(parser);  // <label>
+    insert_element_of_tag_type(
+        parser, GUMBO_TAG_HR, GUMBO_INSERTION_FROM_ISINDEX);
+    pop_current_node(parser);  // <hr>
+    pop_current_node(parser);  // <form>
+    if (!has_open_element(parser, GUMBO_TAG_TEMPLATE)) {
+      parser->_parser_state->_form_element = NULL;
+    }
+    return false;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_TEXTAREA)) {
+    run_generic_parsing_algorithm(parser, token, GUMBO_LEX_RCDATA);
+    parser->_parser_state->_ignore_next_linefeed = true;
+    set_frameset_not_ok(parser);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_XMP)) {
+    bool result = maybe_implicitly_close_p_tag(parser, token);
+    reconstruct_active_formatting_elements(parser);
+    set_frameset_not_ok(parser);
+    run_generic_parsing_algorithm(parser, token, GUMBO_LEX_RAWTEXT);
+    return result;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_IFRAME)) {
+    set_frameset_not_ok(parser);
+    run_generic_parsing_algorithm(parser, token, GUMBO_LEX_RAWTEXT);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_NOEMBED)) {
+    run_generic_parsing_algorithm(parser, token, GUMBO_LEX_RAWTEXT);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_SELECT)) {
+    reconstruct_active_formatting_elements(parser);
+    insert_element_from_token(parser, token);
+    set_frameset_not_ok(parser);
+    GumboInsertionMode state = parser->_parser_state->_insertion_mode;
+    if (state == GUMBO_INSERTION_MODE_IN_TABLE ||
+        state == GUMBO_INSERTION_MODE_IN_CAPTION ||
+        state == GUMBO_INSERTION_MODE_IN_TABLE_BODY ||
+        state == GUMBO_INSERTION_MODE_IN_ROW ||
+        state == GUMBO_INSERTION_MODE_IN_CELL) {
+      set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_SELECT_IN_TABLE);
+    } else {
+      set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_SELECT);
+    }
+    return true;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(OPTION), TAG(OPTGROUP)})) {
+    if (node_html_tag_is(get_current_node(parser), GUMBO_TAG_OPTION)) {
+      pop_current_node(parser);
+    }
+    reconstruct_active_formatting_elements(parser);
+    insert_element_from_token(parser, token);
+    return true;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(RB), TAG(RP), TAG(RT), TAG(RTC)})) {
+    bool success = true;
+    GumboTag exception =
+        tag_in(token, kStartTag, (gumbo_tagset){TAG(RT), TAG(RP)})
+            ? GUMBO_TAG_RTC
+            : GUMBO_TAG_LAST;
+    if (has_an_element_in_scope(parser, GUMBO_TAG_RUBY)) {
+      generate_implied_end_tags(parser, exception);
+    }
+    if (!node_html_tag_is(get_current_node(parser), GUMBO_TAG_RUBY) &&
+        !(exception == GUMBO_TAG_LAST ||
+            node_html_tag_is(get_current_node(parser), GUMBO_TAG_RTC))) {
+      parser_add_parse_error(parser, token);
+      success = false;
+    }
+    insert_element_from_token(parser, token);
+    return success;
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_BR)) {
+    parser_add_parse_error(parser, token);
+    reconstruct_active_formatting_elements(parser);
+    insert_element_of_tag_type(
+        parser, GUMBO_TAG_BR, GUMBO_INSERTION_CONVERTED_FROM_END_TAG);
+    pop_current_node(parser);
+    return false;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_MATH)) {
+    reconstruct_active_formatting_elements(parser);
+    adjust_mathml_attributes(parser, token);
+    adjust_foreign_attributes(parser, token);
+    insert_foreign_element(parser, token, GUMBO_NAMESPACE_MATHML);
+    if (token->v.start_tag.is_self_closing) {
+      pop_current_node(parser);
+      acknowledge_self_closing_tag(parser);
+    }
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_SVG)) {
+    reconstruct_active_formatting_elements(parser);
+    adjust_svg_attributes(parser, token);
+    adjust_foreign_attributes(parser, token);
+    insert_foreign_element(parser, token, GUMBO_NAMESPACE_SVG);
+    if (token->v.start_tag.is_self_closing) {
+      pop_current_node(parser);
+      acknowledge_self_closing_tag(parser);
+    }
+    return true;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(CAPTION), TAG(COL), TAG(COLGROUP),
+                     TAG(FRAME), TAG(HEAD), TAG(TBODY), TAG(TD), TAG(TFOOT),
+                     TAG(TH), TAG(THEAD), TAG(TR)})) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_START_TAG) {
+    reconstruct_active_formatting_elements(parser);
+    insert_element_from_token(parser, token);
+    return true;
+  } else {
+    assert(token->type == GUMBO_TOKEN_END_TAG);
+    GumboTag end_tag = token->v.end_tag;
+    assert(state->_open_elements.length > 0);
+    assert(node_html_tag_is(state->_open_elements.data[0], GUMBO_TAG_HTML));
+    // Walk up the stack of open elements until we find one that either:
+    // a) Matches the tag name we saw
+    // b) Is in the "special" category.
+    // If we see a), implicitly close everything up to and including it.  If we
+    // see b), then record a parse error, don't close anything (except the
+    // implied end tags) and ignore the end tag token.
+    for (int i = state->_open_elements.length; --i >= 0;) {
+      const GumboNode* node = state->_open_elements.data[i];
+      if (node_html_tag_is(node, end_tag)) {
+        generate_implied_end_tags(parser, end_tag);
+        // TODO(jdtang): Do I need to add a parse error here?  The condition in
+        // the spec seems like it's the inverse of the loop condition above, and
+        // so would never fire.
+        while (node != pop_current_node(parser))
+          ;  // Pop everything.
+        return true;
+      } else if (is_special_node(node)) {
+        parser_add_parse_error(parser, token);
+        ignore_token(parser);
+        return false;
+      }
+    }
+    // <html> is in the special category, so we should never get here.
+    assert(0);
+    return false;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-incdata
+static bool handle_text(GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_CHARACTER ||
+      token->type == GUMBO_TOKEN_WHITESPACE) {
+    insert_text_token(parser, token);
+  } else {
+    // We provide only bare-bones script handling that doesn't involve any of
+    // the parser-pause/already-started/script-nesting flags or re-entrant
+    // invocations of the tokenizer.  Because the intended usage of this library
+    // is mostly for templating, refactoring, and static-analysis libraries, we
+    // provide the script body as a text-node child of the <script> element.
+    // This behavior doesn't support document.write of partial HTML elements,
+    // but should be adequate for almost all other scripting support.
+    if (token->type == GUMBO_TOKEN_EOF) {
+      parser_add_parse_error(parser, token);
+      parser->_parser_state->_reprocess_current_token = true;
+    }
+    pop_current_node(parser);
+    set_insertion_mode(parser, parser->_parser_state->_original_insertion_mode);
+  }
+  return true;
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-intable
+static bool handle_in_table(GumboParser* parser, GumboToken* token) {
+  GumboParserState* state = parser->_parser_state;
+  if (token->type == GUMBO_TOKEN_CHARACTER ||
+      token->type == GUMBO_TOKEN_WHITESPACE) {
+    // The "pending table character tokens" list described in the spec is
+    // nothing more than the TextNodeBufferState.  We accumulate text tokens as
+    // normal, except that when we go to flush them in the handle_in_table_text,
+    // we set _foster_parent_insertions if there're non-whitespace characters in
+    // the buffer.
+    assert(state->_text_node._buffer.length == 0);
+    state->_original_insertion_mode = state->_insertion_mode;
+    state->_reprocess_current_token = true;
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE_TEXT);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_current_node(parser), token);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_CAPTION)) {
+    clear_stack_to_table_context(parser);
+    add_formatting_element(parser, &kActiveFormattingScopeMarker);
+    insert_element_from_token(parser, token);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_CAPTION);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_COLGROUP)) {
+    clear_stack_to_table_context(parser);
+    insert_element_from_token(parser, token);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_COLUMN_GROUP);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_COL)) {
+    clear_stack_to_table_context(parser);
+    insert_element_of_tag_type(
+        parser, GUMBO_TAG_COLGROUP, GUMBO_INSERTION_IMPLIED);
+    parser->_parser_state->_reprocess_current_token = true;
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_COLUMN_GROUP);
+    return true;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(TBODY), TAG(TFOOT), TAG(THEAD), TAG(TD),
+                     TAG(TH), TAG(TR)})) {
+    clear_stack_to_table_context(parser);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE_BODY);
+    if (tag_in(token, kStartTag, (gumbo_tagset){TAG(TD), TAG(TH), TAG(TR)})) {
+      insert_element_of_tag_type(
+          parser, GUMBO_TAG_TBODY, GUMBO_INSERTION_IMPLIED);
+      state->_reprocess_current_token = true;
+    } else {
+      insert_element_from_token(parser, token);
+    }
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_TABLE)) {
+    parser_add_parse_error(parser, token);
+    if (close_table(parser)) {
+      parser->_parser_state->_reprocess_current_token = true;
+    } else {
+      ignore_token(parser);
+    }
+    return false;
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_TABLE)) {
+    if (!close_table(parser)) {
+      parser_add_parse_error(parser, token);
+      return false;
+    }
+    return true;
+  } else if (tag_in(token, kEndTag,
+                 (gumbo_tagset){TAG(BODY), TAG(CAPTION), TAG(COL),
+                     TAG(COLGROUP), TAG(HTML), TAG(TBODY), TAG(TD), TAG(TFOOT),
+                     TAG(TH), TAG(THEAD), TAG(TR)})) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(STYLE), TAG(SCRIPT), TAG(TEMPLATE)}) ||
+             (tag_is(token, kEndTag, GUMBO_TAG_TEMPLATE))) {
+    return handle_in_head(parser, token);
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_INPUT) &&
+             attribute_matches(
+                 &token->v.start_tag.attributes, "type", "hidden")) {
+    parser_add_parse_error(parser, token);
+    insert_element_from_token(parser, token);
+    pop_current_node(parser);
+    return false;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_FORM)) {
+    parser_add_parse_error(parser, token);
+    if (state->_form_element || has_open_element(parser, GUMBO_TAG_TEMPLATE)) {
+      ignore_token(parser);
+      return false;
+    }
+    state->_form_element = insert_element_from_token(parser, token);
+    pop_current_node(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_EOF) {
+    return handle_in_body(parser, token);
+  } else {
+    parser_add_parse_error(parser, token);
+    state->_foster_parent_insertions = true;
+    bool result = handle_in_body(parser, token);
+    state->_foster_parent_insertions = false;
+    return result;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-intabletext
+static bool handle_in_table_text(GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_NULL) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_CHARACTER ||
+             token->type == GUMBO_TOKEN_WHITESPACE) {
+    insert_text_token(parser, token);
+    return true;
+  } else {
+    GumboParserState* state = parser->_parser_state;
+    GumboStringBuffer* buffer = &state->_text_node._buffer;
+    // Can't use strspn for this because GumboStringBuffers are not
+    // null-terminated.
+    // Note that TextNodeBuffer may contain UTF-8 characters, but the presence
+    // of any one byte that is not whitespace means we flip the flag, so this
+    // loop is still valid.
+    for (unsigned int i = 0; i < buffer->length; ++i) {
+      if (!isspace((unsigned char) buffer->data[i]) ||
+          buffer->data[i] == '\v') {
+        state->_foster_parent_insertions = true;
+        reconstruct_active_formatting_elements(parser);
+        break;
+      }
+    }
+    maybe_flush_text_node_buffer(parser);
+    state->_foster_parent_insertions = false;
+    state->_reprocess_current_token = true;
+    state->_insertion_mode = state->_original_insertion_mode;
+    return true;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-incaption
+static bool handle_in_caption(GumboParser* parser, GumboToken* token) {
+  if (tag_is(token, kEndTag, GUMBO_TAG_CAPTION)) {
+    if (!has_an_element_in_table_scope(parser, GUMBO_TAG_CAPTION)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    } else {
+      generate_implied_end_tags(parser, GUMBO_TAG_LAST);
+      bool result = true;
+      if (!node_html_tag_is(get_current_node(parser), GUMBO_TAG_CAPTION)) {
+        parser_add_parse_error(parser, token);
+      }
+      while (!node_html_tag_is(pop_current_node(parser), GUMBO_TAG_CAPTION))
+        ;
+      clear_active_formatting_elements(parser);
+      set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE);
+      return result;
+    }
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(CAPTION), TAG(COL), TAG(COLGROUP),
+                     TAG(TBODY), TAG(TD), TAG(TFOOT), TAG(TH), TAG(THEAD),
+                     TAG(TR)}) ||
+             (tag_is(token, kEndTag, GUMBO_TAG_TABLE))) {
+    if (!has_an_element_in_table_scope(parser, GUMBO_TAG_CAPTION)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    while (!node_html_tag_is(pop_current_node(parser), GUMBO_TAG_CAPTION))
+      ;
+    clear_active_formatting_elements(parser);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE);
+    parser->_parser_state->_reprocess_current_token = true;
+    return true;
+  } else if (tag_in(token, kEndTag,
+                 (gumbo_tagset){TAG(BODY), TAG(COL), TAG(COLGROUP), TAG(HTML),
+                     TAG(TBODY), TAG(TD), TAG(TFOOT), TAG(TH), TAG(THEAD),
+                     TAG(TR)})) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else {
+    return handle_in_body(parser, token);
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-incolgroup
+static bool handle_in_column_group(GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_WHITESPACE) {
+    insert_text_token(parser, token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_current_node(parser), token);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HTML)) {
+    return handle_in_body(parser, token);
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_COL)) {
+    insert_element_from_token(parser, token);
+    pop_current_node(parser);
+    acknowledge_self_closing_tag(parser);
+    return true;
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_COLGROUP)) {
+    if (!node_html_tag_is(get_current_node(parser), GUMBO_TAG_COLGROUP)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    pop_current_node(parser);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE);
+    return false;
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_COL)) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_TEMPLATE) ||
+             tag_is(token, kEndTag, GUMBO_TAG_TEMPLATE)) {
+    return handle_in_head(parser, token);
+  } else if (token->type == GUMBO_TOKEN_EOF) {
+    return handle_in_body(parser, token);
+  } else {
+    if (!node_html_tag_is(get_current_node(parser), GUMBO_TAG_COLGROUP)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    pop_current_node(parser);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE);
+    parser->_parser_state->_reprocess_current_token = true;
+    return true;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-intbody
+static bool handle_in_table_body(GumboParser* parser, GumboToken* token) {
+  if (tag_is(token, kStartTag, GUMBO_TAG_TR)) {
+    clear_stack_to_table_body_context(parser);
+    insert_element_from_token(parser, token);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_ROW);
+    return true;
+  } else if (tag_in(token, kStartTag, (gumbo_tagset){TAG(TD), TAG(TH)})) {
+    parser_add_parse_error(parser, token);
+    clear_stack_to_table_body_context(parser);
+    insert_element_of_tag_type(parser, GUMBO_TAG_TR, GUMBO_INSERTION_IMPLIED);
+    parser->_parser_state->_reprocess_current_token = true;
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_ROW);
+    return false;
+  } else if (tag_in(token, kEndTag,
+                 (gumbo_tagset){TAG(TBODY), TAG(TFOOT), TAG(THEAD)})) {
+    if (!has_an_element_in_table_scope(parser, token->v.end_tag)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    clear_stack_to_table_body_context(parser);
+    pop_current_node(parser);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE);
+    return true;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(CAPTION), TAG(COL), TAG(COLGROUP),
+                     TAG(TBODY), TAG(TFOOT), TAG(THEAD)}) ||
+             tag_is(token, kEndTag, GUMBO_TAG_TABLE)) {
+    if (!(has_an_element_in_table_scope(parser, GUMBO_TAG_TBODY) ||
+            has_an_element_in_table_scope(parser, GUMBO_TAG_THEAD) ||
+            has_an_element_in_table_scope(parser, GUMBO_TAG_TFOOT))) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    clear_stack_to_table_body_context(parser);
+    pop_current_node(parser);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE);
+    parser->_parser_state->_reprocess_current_token = true;
+    return true;
+  } else if (tag_in(token, kEndTag,
+                 (gumbo_tagset){TAG(BODY), TAG(CAPTION), TAG(COL), TAG(TR),
+                     TAG(COLGROUP), TAG(HTML), TAG(TD), TAG(TH)})) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else {
+    return handle_in_table(parser, token);
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-intr
+static bool handle_in_row(GumboParser* parser, GumboToken* token) {
+  if (tag_in(token, kStartTag, (gumbo_tagset){TAG(TH), TAG(TD)})) {
+    clear_stack_to_table_row_context(parser);
+    insert_element_from_token(parser, token);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_CELL);
+    add_formatting_element(parser, &kActiveFormattingScopeMarker);
+    return true;
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_TR)) {
+    if (!has_an_element_in_table_scope(parser, GUMBO_TAG_TR)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    } else {
+      clear_stack_to_table_row_context(parser);
+      pop_current_node(parser);
+      set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE_BODY);
+      return true;
+    }
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(CAPTION), TAG(COL), TAG(COLGROUP),
+                     TAG(TBODY), TAG(TFOOT), TAG(THEAD), TAG(TR)}) ||
+             tag_is(token, kEndTag, GUMBO_TAG_TABLE)) {
+    if (!has_an_element_in_table_scope(parser, GUMBO_TAG_TR)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    } else {
+      clear_stack_to_table_row_context(parser);
+      pop_current_node(parser);
+      set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE_BODY);
+      parser->_parser_state->_reprocess_current_token = true;
+      return true;
+    }
+  } else if (tag_in(token, kEndTag,
+                 (gumbo_tagset){TAG(TBODY), TAG(TFOOT), TAG(THEAD)})) {
+    if (!has_an_element_in_table_scope(parser, token->v.end_tag) ||
+        (!has_an_element_in_table_scope(parser, GUMBO_TAG_TR))) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    } else {
+      clear_stack_to_table_row_context(parser);
+      pop_current_node(parser);
+      set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE_BODY);
+      parser->_parser_state->_reprocess_current_token = true;
+      return true;
+    }
+  } else if (tag_in(token, kEndTag,
+                 (gumbo_tagset){TAG(BODY), TAG(CAPTION), TAG(COL),
+                     TAG(COLGROUP), TAG(HTML), TAG(TD), TAG(TH)})) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else {
+    return handle_in_table(parser, token);
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-intd
+static bool handle_in_cell(GumboParser* parser, GumboToken* token) {
+  if (tag_in(token, kEndTag, (gumbo_tagset){TAG(TD), TAG(TH)})) {
+    GumboTag token_tag = token->v.end_tag;
+    if (!has_an_element_in_table_scope(parser, token_tag)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    return close_table_cell(parser, token, token_tag);
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(CAPTION), TAG(COL), TAG(COLGROUP),
+                     TAG(TBODY), TAG(TD), TAG(TFOOT), TAG(TH), TAG(THEAD),
+                     TAG(TR)})) {
+    gumbo_debug("Handling <td> in cell.\n");
+    if (!has_an_element_in_table_scope(parser, GUMBO_TAG_TH) &&
+        !has_an_element_in_table_scope(parser, GUMBO_TAG_TD)) {
+      gumbo_debug("Bailing out because there's no <td> or <th> in scope.\n");
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    parser->_parser_state->_reprocess_current_token = true;
+    return close_current_cell(parser, token);
+  } else if (tag_in(token, kEndTag, (gumbo_tagset){TAG(BODY), TAG(CAPTION),
+                                        TAG(COL), TAG(COLGROUP), TAG(HTML)})) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (tag_in(token, kEndTag, (gumbo_tagset){TAG(TABLE), TAG(TBODY),
+                                        TAG(TFOOT), TAG(THEAD), TAG(TR)})) {
+    if (!has_an_element_in_table_scope(parser, token->v.end_tag)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    parser->_parser_state->_reprocess_current_token = true;
+    return close_current_cell(parser, token);
+  } else {
+    return handle_in_body(parser, token);
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-inselect
+static bool handle_in_select(GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_NULL) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_CHARACTER ||
+             token->type == GUMBO_TOKEN_WHITESPACE) {
+    insert_text_token(parser, token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_current_node(parser), token);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HTML)) {
+    return handle_in_body(parser, token);
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_OPTION)) {
+    if (node_html_tag_is(get_current_node(parser), GUMBO_TAG_OPTION)) {
+      pop_current_node(parser);
+    }
+    insert_element_from_token(parser, token);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_OPTGROUP)) {
+    if (node_html_tag_is(get_current_node(parser), GUMBO_TAG_OPTION)) {
+      pop_current_node(parser);
+    }
+    if (node_html_tag_is(get_current_node(parser), GUMBO_TAG_OPTGROUP)) {
+      pop_current_node(parser);
+    }
+    insert_element_from_token(parser, token);
+    return true;
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_OPTGROUP)) {
+    GumboVector* open_elements = &parser->_parser_state->_open_elements;
+    if (node_html_tag_is(get_current_node(parser), GUMBO_TAG_OPTION) &&
+        node_html_tag_is(open_elements->data[open_elements->length - 2],
+            GUMBO_TAG_OPTGROUP)) {
+      pop_current_node(parser);
+    }
+    if (node_html_tag_is(get_current_node(parser), GUMBO_TAG_OPTGROUP)) {
+      pop_current_node(parser);
+      return true;
+    } else {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_OPTION)) {
+    if (node_html_tag_is(get_current_node(parser), GUMBO_TAG_OPTION)) {
+      pop_current_node(parser);
+      return true;
+    } else {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_SELECT)) {
+    if (!has_an_element_in_select_scope(parser, GUMBO_TAG_SELECT)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    close_current_select(parser);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_SELECT)) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    if (has_an_element_in_select_scope(parser, GUMBO_TAG_SELECT)) {
+      close_current_select(parser);
+    }
+    return false;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(INPUT), TAG(KEYGEN), TAG(TEXTAREA)})) {
+    parser_add_parse_error(parser, token);
+    if (!has_an_element_in_select_scope(parser, GUMBO_TAG_SELECT)) {
+      ignore_token(parser);
+    } else {
+      close_current_select(parser);
+      parser->_parser_state->_reprocess_current_token = true;
+    }
+    return false;
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(SCRIPT), TAG(TEMPLATE)}) ||
+             tag_is(token, kEndTag, GUMBO_TAG_TEMPLATE)) {
+    return handle_in_head(parser, token);
+  } else if (token->type == GUMBO_TOKEN_EOF) {
+    return handle_in_body(parser, token);
+  } else {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-inselectintable
+static bool handle_in_select_in_table(GumboParser* parser, GumboToken* token) {
+  if (tag_in(token, kStartTag,
+          (gumbo_tagset){TAG(CAPTION), TAG(TABLE), TAG(TBODY), TAG(TFOOT),
+              TAG(THEAD), TAG(TR), TAG(TD), TAG(TH)})) {
+    parser_add_parse_error(parser, token);
+    close_current_select(parser);
+    parser->_parser_state->_reprocess_current_token = true;
+    return false;
+  } else if (tag_in(token, kEndTag,
+                 (gumbo_tagset){TAG(CAPTION), TAG(TABLE), TAG(TBODY),
+                     TAG(TFOOT), TAG(THEAD), TAG(TR), TAG(TD), TAG(TH)})) {
+    parser_add_parse_error(parser, token);
+    if (!has_an_element_in_table_scope(parser, token->v.end_tag)) {
+      ignore_token(parser);
+      return false;
+    } else {
+      close_current_select(parser);
+      // close_current_select already does the
+      // reset_insertion_mode_appropriately
+      // reset_insertion_mode_appropriately(parser);
+      parser->_parser_state->_reprocess_current_token = true;
+      return false;
+    }
+  } else {
+    return handle_in_select(parser, token);
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/multipage/tree-construction.html#parsing-main-intemplate
+static bool handle_in_template(GumboParser* parser, GumboToken* token) {
+  GumboParserState* state = parser->_parser_state;
+  if (token->type == GUMBO_TOKEN_WHITESPACE ||
+      token->type == GUMBO_TOKEN_CHARACTER ||
+      token->type == GUMBO_TOKEN_COMMENT || token->type == GUMBO_TOKEN_NULL ||
+      token->type == GUMBO_TOKEN_DOCTYPE) {
+    return handle_in_body(parser, token);
+  } else if (tag_in(token, kStartTag,
+                 (gumbo_tagset){TAG(BASE), TAG(BASEFONT), TAG(BGSOUND),
+                     TAG(LINK), TAG(META), TAG(NOFRAMES), TAG(SCRIPT),
+                     TAG(STYLE), TAG(TEMPLATE), TAG(TITLE)}) ||
+             tag_is(token, kEndTag, GUMBO_TAG_TEMPLATE)) {
+    return handle_in_head(parser, token);
+  } else if (tag_in(
+                 token, kStartTag, (gumbo_tagset){TAG(CAPTION), TAG(COLGROUP),
+                                       TAG(TBODY), TAG(TFOOT), TAG(THEAD)})) {
+    pop_template_insertion_mode(parser);
+    push_template_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE);
+    state->_reprocess_current_token = true;
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_COL)) {
+    pop_template_insertion_mode(parser);
+    push_template_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_COLUMN_GROUP);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_COLUMN_GROUP);
+    state->_reprocess_current_token = true;
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_TR)) {
+    pop_template_insertion_mode(parser);
+    push_template_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE_BODY);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TABLE_BODY);
+    state->_reprocess_current_token = true;
+    return true;
+  } else if (tag_in(token, kStartTag, (gumbo_tagset){TAG(TD), TAG(TH)})) {
+    pop_template_insertion_mode(parser);
+    push_template_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_ROW);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_ROW);
+    state->_reprocess_current_token = true;
+    return true;
+  } else if (token->type == GUMBO_TOKEN_START_TAG) {
+    pop_template_insertion_mode(parser);
+    push_template_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_BODY);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_BODY);
+    state->_reprocess_current_token = true;
+    return true;
+  } else if (token->type == GUMBO_TOKEN_END_TAG) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (token->type == GUMBO_TOKEN_EOF) {
+    if (!has_open_element(parser, GUMBO_TAG_TEMPLATE)) {
+      // Stop parsing.
+      return true;
+    }
+    parser_add_parse_error(parser, token);
+    while (!node_html_tag_is(pop_current_node(parser), GUMBO_TAG_TEMPLATE))
+      ;
+    clear_active_formatting_elements(parser);
+    pop_template_insertion_mode(parser);
+    reset_insertion_mode_appropriately(parser);
+    state->_reprocess_current_token = true;
+    return false;
+  } else {
+    assert(0);
+    return false;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-afterbody
+static bool handle_after_body(GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_WHITESPACE ||
+      tag_is(token, kStartTag, GUMBO_TAG_HTML)) {
+    return handle_in_body(parser, token);
+  } else if (token->type == GUMBO_TOKEN_COMMENT) {
+    GumboNode* html_node = parser->_output->root;
+    assert(html_node != NULL);
+    append_comment_node(parser, html_node, token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_HTML)) {
+    /* fragment case: ignore the closing HTML token */
+    if (is_fragment_parser(parser)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_AFTER_AFTER_BODY);
+    GumboNode* html = parser->_parser_state->_open_elements.data[0];
+    assert(node_html_tag_is(html, GUMBO_TAG_HTML));
+    record_end_of_element(
+        parser->_parser_state->_current_token, &html->v.element);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_EOF) {
+    return true;
+  } else {
+    parser_add_parse_error(parser, token);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_BODY);
+    parser->_parser_state->_reprocess_current_token = true;
+    return false;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-inframeset
+static bool handle_in_frameset(GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_WHITESPACE) {
+    insert_text_token(parser, token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_current_node(parser), token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HTML)) {
+    return handle_in_body(parser, token);
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_FRAMESET)) {
+    insert_element_from_token(parser, token);
+    return true;
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_FRAMESET)) {
+    if (node_html_tag_is(get_current_node(parser), GUMBO_TAG_HTML)) {
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    }
+    pop_current_node(parser);
+    if (!is_fragment_parser(parser) &&
+        !node_html_tag_is(get_current_node(parser), GUMBO_TAG_FRAMESET)) {
+      set_insertion_mode(parser, GUMBO_INSERTION_MODE_AFTER_FRAMESET);
+    }
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_FRAME)) {
+    insert_element_from_token(parser, token);
+    pop_current_node(parser);
+    acknowledge_self_closing_tag(parser);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_NOFRAMES)) {
+    return handle_in_head(parser, token);
+  } else if (token->type == GUMBO_TOKEN_EOF) {
+    if (!node_html_tag_is(get_current_node(parser), GUMBO_TAG_HTML)) {
+      parser_add_parse_error(parser, token);
+      return false;
+    }
+    return true;
+  } else {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-afterframeset
+static bool handle_after_frameset(GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_WHITESPACE) {
+    insert_text_token(parser, token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_current_node(parser), token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_DOCTYPE) {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_HTML)) {
+    return handle_in_body(parser, token);
+  } else if (tag_is(token, kEndTag, GUMBO_TAG_HTML)) {
+    GumboNode* html = parser->_parser_state->_open_elements.data[0];
+    assert(node_html_tag_is(html, GUMBO_TAG_HTML));
+    record_end_of_element(
+        parser->_parser_state->_current_token, &html->v.element);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_AFTER_AFTER_FRAMESET);
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_NOFRAMES)) {
+    return handle_in_head(parser, token);
+  } else if (token->type == GUMBO_TOKEN_EOF) {
+    return true;
+  } else {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#the-after-after-body-insertion-mode
+static bool handle_after_after_body(GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_document_node(parser), token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_DOCTYPE ||
+             token->type == GUMBO_TOKEN_WHITESPACE ||
+             tag_is(token, kStartTag, GUMBO_TAG_HTML)) {
+    return handle_in_body(parser, token);
+  } else if (token->type == GUMBO_TOKEN_EOF) {
+    return true;
+  } else {
+    parser_add_parse_error(parser, token);
+    set_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_BODY);
+    parser->_parser_state->_reprocess_current_token = true;
+    return false;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#the-after-after-frameset-insertion-mode
+static bool handle_after_after_frameset(
+    GumboParser* parser, GumboToken* token) {
+  if (token->type == GUMBO_TOKEN_COMMENT) {
+    append_comment_node(parser, get_document_node(parser), token);
+    return true;
+  } else if (token->type == GUMBO_TOKEN_DOCTYPE ||
+             token->type == GUMBO_TOKEN_WHITESPACE ||
+             tag_is(token, kStartTag, GUMBO_TAG_HTML)) {
+    return handle_in_body(parser, token);
+  } else if (token->type == GUMBO_TOKEN_EOF) {
+    return true;
+  } else if (tag_is(token, kStartTag, GUMBO_TAG_NOFRAMES)) {
+    return handle_in_head(parser, token);
+  } else {
+    parser_add_parse_error(parser, token);
+    ignore_token(parser);
+    return false;
+  }
+}
+
+// Function pointers for each insertion mode.  Keep in sync with
+// insertion_mode.h.
+typedef bool (*TokenHandler)(GumboParser* parser, GumboToken* token);
+static const TokenHandler kTokenHandlers[] = {handle_initial,
+    handle_before_html, handle_before_head, handle_in_head,
+    handle_in_head_noscript, handle_after_head, handle_in_body, handle_text,
+    handle_in_table, handle_in_table_text, handle_in_caption,
+    handle_in_column_group, handle_in_table_body, handle_in_row, handle_in_cell,
+    handle_in_select, handle_in_select_in_table, handle_in_template,
+    handle_after_body, handle_in_frameset, handle_after_frameset,
+    handle_after_after_body, handle_after_after_frameset};
+
+static bool handle_html_content(GumboParser* parser, GumboToken* token) {
+  return kTokenHandlers[(unsigned int) parser->_parser_state->_insertion_mode](
+      parser, token);
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/complete/tokenization.html#parsing-main-inforeign
+static bool handle_in_foreign_content(GumboParser* parser, GumboToken* token) {
+  gumbo_debug("Handling foreign content");
+  switch (token->type) {
+    case GUMBO_TOKEN_NULL:
+      parser_add_parse_error(parser, token);
+      token->v.character = kUtf8ReplacementChar;
+      insert_text_token(parser, token);
+      return false;
+    case GUMBO_TOKEN_WHITESPACE:
+      insert_text_token(parser, token);
+      return true;
+    case GUMBO_TOKEN_CDATA:
+    case GUMBO_TOKEN_CHARACTER:
+      insert_text_token(parser, token);
+      set_frameset_not_ok(parser);
+      return true;
+    case GUMBO_TOKEN_COMMENT:
+      append_comment_node(parser, get_current_node(parser), token);
+      return true;
+    case GUMBO_TOKEN_DOCTYPE:
+      parser_add_parse_error(parser, token);
+      ignore_token(parser);
+      return false;
+    default:
+      // Fall through to the if-statements below.
+      break;
+  }
+  // Order matters for these clauses.
+  if (tag_in(token, kStartTag,
+          (gumbo_tagset){TAG(B), TAG(BIG), TAG(BLOCKQUOTE), TAG(BODY), TAG(BR),
+              TAG(CENTER), TAG(CODE), TAG(DD), TAG(DIV), TAG(DL), TAG(DT),
+              TAG(EM), TAG(EMBED), TAG(H1), TAG(H2), TAG(H3), TAG(H4), TAG(H5),
+              TAG(H6), TAG(HEAD), TAG(HR), TAG(I), TAG(IMG), TAG(LI),
+              TAG(LISTING), TAG(MENU), TAG(META), TAG(NOBR), TAG(OL), TAG(P),
+              TAG(PRE), TAG(RUBY), TAG(S), TAG(SMALL), TAG(SPAN), TAG(STRONG),
+              TAG(STRIKE), TAG(SUB), TAG(SUP), TAG(TABLE), TAG(TT), TAG(U),
+              TAG(UL), TAG(VAR)}) ||
+      (tag_is(token, kStartTag, GUMBO_TAG_FONT) &&
+          (token_has_attribute(token, "color") ||
+              token_has_attribute(token, "face") ||
+              token_has_attribute(token, "size")))) {
+    /* Parse error */
+    parser_add_parse_error(parser, token);
+
+    /*
+     * Fragment case: If the parser was originally created for the HTML
+     * fragment parsing algorithm, then act as described in the "any other
+     * start tag" entry below.
+     */
+    if (!is_fragment_parser(parser)) {
+      do {
+        pop_current_node(parser);
+      } while (!(is_mathml_integration_point(get_current_node(parser)) ||
+                   is_html_integration_point(get_current_node(parser)) ||
+                   get_current_node(parser)->v.element.tag_namespace ==
+                       GUMBO_NAMESPACE_HTML));
+      parser->_parser_state->_reprocess_current_token = true;
+      return false;
+    }
+
+    assert(token->type == GUMBO_TOKEN_START_TAG);
+  }
+
+  if (token->type == GUMBO_TOKEN_START_TAG) {
+    const GumboNamespaceEnum current_namespace =
+        get_adjusted_current_node(parser)->v.element.tag_namespace;
+    if (current_namespace == GUMBO_NAMESPACE_MATHML) {
+      adjust_mathml_attributes(parser, token);
+    }
+    if (current_namespace == GUMBO_NAMESPACE_SVG) {
+      // Tag adjustment is left to the gumbo_normalize_svg_tagname helper
+      // function.
+      adjust_svg_attributes(parser, token);
+    }
+    adjust_foreign_attributes(parser, token);
+    insert_foreign_element(parser, token, current_namespace);
+    if (token->v.start_tag.is_self_closing) {
+      pop_current_node(parser);
+      acknowledge_self_closing_tag(parser);
+    }
+    return true;
+    // </script> tags are handled like any other end tag, putting the script's
+    // text into a text node child and closing the current node.
+  } else {
+    assert(token->type == GUMBO_TOKEN_END_TAG);
+    GumboNode* node = get_current_node(parser);
+    assert(node != NULL);
+    GumboStringPiece token_tagname = token->original_text;
+    GumboStringPiece node_tagname = node->v.element.original_tag;
+    gumbo_tag_from_original_text(&token_tagname);
+    gumbo_tag_from_original_text(&node_tagname);
+
+    bool is_success = true;
+    if (!gumbo_string_equals_ignore_case(&node_tagname, &token_tagname)) {
+      parser_add_parse_error(parser, token);
+      is_success = false;
+    }
+    int i = parser->_parser_state->_open_elements.length;
+    for (--i; i > 0;) {
+      // Here we move up the stack until we find an HTML element (in which
+      // case we do nothing) or we find the element that we're about to
+      // close (in which case we pop everything we've seen until that
+      // point.)
+      gumbo_debug("Foreign %.*s node at %d.\n", node_tagname.length,
+          node_tagname.data, i);
+      if (gumbo_string_equals_ignore_case(&node_tagname, &token_tagname)) {
+        gumbo_debug("Matches.\n");
+        while (pop_current_node(parser) != node) {
+          // Pop all the nodes below the current one.  Node is guaranteed to
+          // be an element on the stack of open elements (set below), so
+          // this loop is guaranteed to terminate.
+        }
+        return is_success;
+      }
+      --i;
+      node = parser->_parser_state->_open_elements.data[i];
+      if (node->v.element.tag_namespace == GUMBO_NAMESPACE_HTML) {
+        // Must break before gumbo_tag_from_original_text to avoid passing
+        // parser-inserted nodes through.
+        break;
+      }
+      node_tagname = node->v.element.original_tag;
+      gumbo_tag_from_original_text(&node_tagname);
+    }
+    assert(node->v.element.tag_namespace == GUMBO_NAMESPACE_HTML);
+    // We can't call handle_token directly because the current node is still in
+    // the SVG namespace, so it would re-enter this and result in infinite
+    // recursion.
+    return handle_html_content(parser, token) && is_success;
+  }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/multipage/tree-construction.html#tree-construction
+static bool handle_token(GumboParser* parser, GumboToken* token) {
+  if (parser->_parser_state->_ignore_next_linefeed &&
+      token->type == GUMBO_TOKEN_WHITESPACE && token->v.character == '\n') {
+    parser->_parser_state->_ignore_next_linefeed = false;
+    ignore_token(parser);
+    return true;
+  }
+  // This needs to be reset both here and in the conditional above to catch both
+  // the case where the next token is not whitespace (so we don't ignore
+  // whitespace in the middle of <pre> tags) and where there are multiple
+  // whitespace tokens (so we don't ignore the second one).
+  parser->_parser_state->_ignore_next_linefeed = false;
+
+  if (tag_is(token, kEndTag, GUMBO_TAG_BODY)) {
+    parser->_parser_state->_closed_body_tag = true;
+  }
+  if (tag_is(token, kEndTag, GUMBO_TAG_HTML)) {
+    parser->_parser_state->_closed_html_tag = true;
+  }
+
+  const GumboNode* current_node = get_adjusted_current_node(parser);
+  assert(!current_node || current_node->type == GUMBO_NODE_ELEMENT ||
+         current_node->type == GUMBO_NODE_TEMPLATE);
+  if (current_node) {
+    gumbo_debug("Current node: <%s>.\n",
+        gumbo_normalized_tagname(current_node->v.element.tag));
+  }
+  if (!current_node ||
+      current_node->v.element.tag_namespace == GUMBO_NAMESPACE_HTML ||
+      (is_mathml_integration_point(current_node) &&
+          (token->type == GUMBO_TOKEN_CHARACTER ||
+              token->type == GUMBO_TOKEN_WHITESPACE ||
+              token->type == GUMBO_TOKEN_NULL ||
+              (token->type == GUMBO_TOKEN_START_TAG &&
+                  !tag_in(token, kStartTag,
+                      (gumbo_tagset){TAG(MGLYPH), TAG(MALIGNMARK)})))) ||
+      (current_node->v.element.tag_namespace == GUMBO_NAMESPACE_MATHML &&
+          node_qualified_tag_is(
+              current_node, GUMBO_NAMESPACE_MATHML, GUMBO_TAG_ANNOTATION_XML) &&
+          tag_is(token, kStartTag, GUMBO_TAG_SVG)) ||
+      (is_html_integration_point(current_node) &&
+          (token->type == GUMBO_TOKEN_START_TAG ||
+              token->type == GUMBO_TOKEN_CHARACTER ||
+              token->type == GUMBO_TOKEN_NULL ||
+              token->type == GUMBO_TOKEN_WHITESPACE)) ||
+      token->type == GUMBO_TOKEN_EOF) {
+    return handle_html_content(parser, token);
+  } else {
+    return handle_in_foreign_content(parser, token);
+  }
+}
+
+static void fragment_parser_init(GumboParser* parser, GumboTag fragment_ctx,
+    GumboNamespaceEnum fragment_namespace) {
+  GumboNode* root;
+  assert(fragment_ctx != GUMBO_TAG_LAST);
+
+  // 3
+  parser->_parser_state->_fragment_ctx = create_element(parser, fragment_ctx);
+  parser->_parser_state->_fragment_ctx->v.element.tag_namespace =
+      fragment_namespace;
+
+  // 4
+  if (fragment_namespace == GUMBO_NAMESPACE_HTML) {
+    // Non-HTML namespaces always start in the DATA state.
+    switch (fragment_ctx) {
+      case GUMBO_TAG_TITLE:
+      case GUMBO_TAG_TEXTAREA:
+        gumbo_tokenizer_set_state(parser, GUMBO_LEX_RCDATA);
+        break;
+
+      case GUMBO_TAG_STYLE:
+      case GUMBO_TAG_XMP:
+      case GUMBO_TAG_IFRAME:
+      case GUMBO_TAG_NOEMBED:
+      case GUMBO_TAG_NOFRAMES:
+        gumbo_tokenizer_set_state(parser, GUMBO_LEX_RAWTEXT);
+        break;
+
+      case GUMBO_TAG_SCRIPT:
+        gumbo_tokenizer_set_state(parser, GUMBO_LEX_SCRIPT);
+        break;
+
+      case GUMBO_TAG_NOSCRIPT:
+        /* scripting is disabled in Gumbo, so leave the tokenizer
+         * in the default data state */
+        break;
+
+      case GUMBO_TAG_PLAINTEXT:
+        gumbo_tokenizer_set_state(parser, GUMBO_LEX_PLAINTEXT);
+        break;
+
+      default:
+        /* default data state */
+        break;
+    }
+  }
+
+  // 5. 6. 7.
+  root = insert_element_of_tag_type(
+      parser, GUMBO_TAG_HTML, GUMBO_INSERTION_IMPLIED);
+  parser->_output->root = root;
+
+  // 8.
+  if (fragment_ctx == GUMBO_TAG_TEMPLATE) {
+    push_template_insertion_mode(parser, GUMBO_INSERTION_MODE_IN_TEMPLATE);
+  }
+
+  // 10.
+  reset_insertion_mode_appropriately(parser);
+}
+
+GumboOutput* gumbo_parse(const char* buffer) {
+  return gumbo_parse_with_options(
+      &kGumboDefaultOptions, buffer, strlen(buffer));
+}
+
+GumboOutput* gumbo_parse_with_options(
+    const GumboOptions* options, const char* buffer, size_t length) {
+  GumboParser parser;
+  parser._options = options;
+  output_init(&parser);
+  gumbo_tokenizer_state_init(&parser, buffer, length);
+  parser_state_init(&parser);
+
+  if (options->fragment_context != GUMBO_TAG_LAST) {
+    fragment_parser_init(
+        &parser, options->fragment_context, options->fragment_namespace);
+  }
+
+  GumboParserState* state = parser._parser_state;
+  gumbo_debug("Parsing %.*s.\n", length, buffer);
+
+  // Sanity check so that infinite loops die with an assertion failure instead
+  // of hanging the process before we ever get an error.
+  int loop_count = 0;
+
+  GumboToken token;
+  bool has_error = false;
+
+  do {
+    if (state->_reprocess_current_token) {
+      state->_reprocess_current_token = false;
+    } else {
+      GumboNode* current_node = get_current_node(&parser);
+      gumbo_tokenizer_set_is_current_node_foreign(&parser,
+          current_node &&
+              current_node->v.element.tag_namespace != GUMBO_NAMESPACE_HTML);
+      has_error = !gumbo_lex(&parser, &token) || has_error;
+    }
+    const char* token_type = "text";
+    switch (token.type) {
+      case GUMBO_TOKEN_DOCTYPE:
+        token_type = "doctype";
+        break;
+      case GUMBO_TOKEN_START_TAG:
+        token_type = gumbo_normalized_tagname(token.v.start_tag.tag);
+        break;
+      case GUMBO_TOKEN_END_TAG:
+        token_type = gumbo_normalized_tagname(token.v.end_tag);
+        break;
+      case GUMBO_TOKEN_COMMENT:
+        token_type = "comment";
+        break;
+      default:
+        break;
+    }
+    gumbo_debug("Handling %s token @%d:%d in state %d.\n", (char*) token_type,
+        token.position.line, token.position.column, state->_insertion_mode);
+
+    state->_current_token = &token;
+    state->_self_closing_flag_acknowledged =
+        !(token.type == GUMBO_TOKEN_START_TAG &&
+            token.v.start_tag.is_self_closing);
+
+    has_error = !handle_token(&parser, &token) || has_error;
+
+    // Check for memory leaks when ownership is transferred from start tag
+    // tokens to nodes.
+    assert(state->_reprocess_current_token ||
+           token.type != GUMBO_TOKEN_START_TAG ||
+           token.v.start_tag.attributes.data == NULL);
+
+    if (!state->_self_closing_flag_acknowledged) {
+      GumboError* error = parser_add_parse_error(&parser, &token);
+      if (error) {
+        error->type = GUMBO_ERR_UNACKNOWLEDGED_SELF_CLOSING_TAG;
+      }
+    }
+
+    ++loop_count;
+    assert(loop_count < 1000000000);
+
+  } while ((token.type != GUMBO_TOKEN_EOF || state->_reprocess_current_token) &&
+           !(options->stop_on_first_error && has_error));
+
+  finish_parsing(&parser);
+  // For API uniformity reasons, if the doctype still has nulls, convert them to
+  // empty strings.
+  GumboDocument* doc_type = &parser._output->document->v.document;
+  if (doc_type->name == NULL) {
+    doc_type->name = gumbo_copy_stringz(&parser, "");
+  }
+  if (doc_type->public_identifier == NULL) {
+    doc_type->public_identifier = gumbo_copy_stringz(&parser, "");
+  }
+  if (doc_type->system_identifier == NULL) {
+    doc_type->system_identifier = gumbo_copy_stringz(&parser, "");
+  }
+
+  parser_state_destroy(&parser);
+  gumbo_tokenizer_state_destroy(&parser);
+  return parser._output;
+}
+
+void gumbo_destroy_node(GumboOptions* options, GumboNode* node) {
+  // Need a dummy GumboParser because the allocator comes along with the
+  // options object.
+  GumboParser parser;
+  parser._options = options;
+  destroy_node(&parser, node);
+}
+
+void gumbo_destroy_output(const GumboOptions* options, GumboOutput* output) {
+  // Need a dummy GumboParser because the allocator comes along with the
+  // options object.
+  GumboParser parser;
+  parser._options = options;
+  destroy_node(&parser, output->document);
+  for (unsigned int i = 0; i < output->errors.length; ++i) {
+    gumbo_error_destroy(&parser, output->errors.data[i]);
+  }
+  gumbo_vector_destroy(&parser, &output->errors);
+  gumbo_parser_deallocate(&parser, output);
+}