Clarified that urlize and urlizetrunc should only be applied to plain text. Refs #5202.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@5937 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/templates.txt

@@ -1326,12 +1326,17 @@ urlize
 
 Converts URLs in plain text into clickable links.
 
+Note that if ``urlize`` is applied to text that already contains HTML markup,
+things won't work as expected. Apply this filter only to *plain* text.
+
 urlizetrunc
 ~~~~~~~~~~~
 
 Converts URLs into clickable links, truncating URLs longer than the given
 character limit.
 
+As with urlize_, this filter should only be applied to *plain* text.
+
 **Argument:** Length to truncate URLs to
 
 wordcount