--- a/bin/check-ports	Wed Sep 25 09:43:46 2019 +0200
+++ b/bin/check-ports	Wed Sep 25 09:44:04 2019 +0200
@@ -257,6 +257,30 @@
 }
 
 get_mapping() {
+    : 'Determine whether a package `_package` is essentially the same as
+    another package.
+
+    Args:
+        _package: the new name of the package
+
+    Returns:
+        0 when a package mapping has been found, 1 otherwise
+
+    Output (Globals):
+        mapped_package_name: the name of the package on which `_package` is
+                             based on
+
+    This command reads from the mapping database in in file
+    `/usr/local/etc/local-bsdtools/package-mapping.conf`.
+    Example::
+
+        #
+        # _package                         mapped_package_name
+        #
+        fmg-nextcloud-php71                nextcloud-php71
+        fmg-nextcloud-twofactor_totp-php71 nextcloud-twofactor_totp-php71
+
+    '
     local _package _n _mapped
 
     _package=$1