--- a/configmix/__init__.py	Sat Mar 24 16:04:52 2018 +0100
+++ b/configmix/__init__.py	Sat Mar 24 16:06:08 2018 +0100
@@ -82,39 +82,53 @@
         return result
 
 
-def merge(user, default, _first=True):
-    """A simple (YAML-)tree-merge.
+def merge(user, default):
+    """Logically merge the configuration in `user` into `default`.
 
     :param ~configmix.config.Configuration user:
-                the new configuration that will be merged into `default`
+                the new configuration that will be logically merged
+                into `default`
     :param ~configmix.config.Configuration default:
-                the base configuration where `user` is merged into
-    :param bool _first: an intexrnal argument for controlling recursion
+                the base configuration where `user` is logically merged into
+    :returns: `user` with the necessary amendments from `default`.
+              If `user` is ``None`` then `default` is returned.
+
+    .. note:: The configuration in `default` is not changed but the
+              configuration given in `user` is changed **inplace**.
 
     From http://stackoverflow.com/questions/823196/yaml-merge-in-python
 
-    .. note:: `_first` is an internal argument.
-
     """
-    if _first and (user is None):
+    if user is None:
         return default
     if isinstance(user, dict) and isinstance(default, dict):
         for k, v in default.items():
             if k not in user:
                 user[k] = v
             else:
-                user[k] = merge(user[k], v, False)
+                user[k] = _merge(user[k], v)
     return user
 
 
-def safe_merge(user, default, _first=True):
-    """A more safe version of :func:`merge()` that makes shallow copies of
+def _merge(user, default):
+    """Recursion helper for :meth:`merge`
+
+    """
+    if isinstance(user, dict) and isinstance(default, dict):
+        for k, v in default.items():
+            if k not in user:
+                user[k] = v
+            else:
+                user[k] = _merge(user[k], v)
+    return user
+
+
+def safe_merge(user, default):
+    """A more safe version of :func:`merge` that makes shallow copies of
     the returned container objects.
 
-    .. note:: `_first` is an internal argument.
-
     """
-    if _first and (user is None):
+    if user is None:
         return copy.copy(default)
     user = copy.copy(user)
     if isinstance(user, dict) and isinstance(default, dict):
@@ -122,5 +136,5 @@
             if k not in user:
                 user[k] = copy.copy(v)
             else:
-                user[k] = merge(user[k], v, False)
+                user[k] = _merge(user[k], v)
     return user