diff --git a/docs/quickstart.rst b/docs/quickstart.rst
index 4be9a63f..59e36bcc 100644
--- a/docs/quickstart.rst
+++ b/docs/quickstart.rst
@@ -160,6 +160,8 @@ The following converters exist:
 `path`      like the default but also accepts slashes
 =========== ===========================================
 
+.. _url-building:
+
 URL Building
 ````````````
 
@@ -167,7 +169,8 @@ If it can match URLs, can it also generate them?  Of course you can.  To
 build a URL to a specific function you can use the :func:`~flask.url_for`
 function.  It accepts the name of the function as first argument and a
 number of keyword arguments, each corresponding to the variable part of
-the URL rule.  Here some examples:
+the URL rule.  Unknown variable parts are appended to the URL as query
+parameter.  Here some examples:
 
 >>> from flask import Flask, url_for
 >>> app = Flask(__name__)
@@ -184,9 +187,11 @@ the URL rule.  Here some examples:
 ...  print url_for('index')
 ...  print url_for('login')
 ...  print url_for('profile', username='John Doe')
+...  print url_for('login', next='/')
 ... 
 /
 /login
+/login?next=/
 /user/John%20Doe
 
 (This also uses the :meth:`~flask.Flask.test_request_context` method
diff --git a/flask.py b/flask.py
index 32b690ca..c1c3fdb7 100644
--- a/flask.py
+++ b/flask.py
@@ -145,6 +145,10 @@ class _RequestContext(object):
 
 def url_for(endpoint, **values):
     """Generates a URL to the given endpoint with the method provided.
+    Variable arguments that are unknown to the target endpoint are appended
+    to the generated URL as query arguments.
+
+    For more information, head over to the :ref:`Quickstart <url-building>`.
 
     :param endpoint: the endpoint of the URL (name of the function)
     :param values: the variable arguments of the URL rule