Doc improvements for url_for()
diff --git a/flask/helpers.py b/flask/helpers.py
index 501a2f811c..7e20c97d47 100644
--- a/flask/helpers.py
+++ b/flask/helpers.py
@@ -113,7 +113,7 @@ def generate():
                 yield '!'
             return Response(generate())
 
-    Alternatively it can also be used around a specific generator:
+    Alternatively it can also be used around a specific generator::
 
         from flask import stream_with_context, request, Response
 
@@ -305,7 +305,9 @@ def external_url_handler(error, endpoint, **values):
 
     :param endpoint: the endpoint of the URL (name of the function)
     :param values: the variable arguments of the URL rule
-    :param _external: if set to `True`, an absolute URL is generated.
+    :param _external: if set to `True`, an absolute URL is generated. Server
+      address can be changed via `SERVER_NAME` configuration variable which
+      defaults to `localhost`.
     :param _anchor: if provided this is added as anchor to the URL.
     :param _method: if provided this explicitly specifies an HTTP method.
     """

Recently I had to ask from IRC how to generate proper full url using `url_for()`, so I think that its docs should at least mention `SERVER_NAME`.

Also fixes a formatting error in another docstring.
