Added some links in /docs/intro/overview.txt

Thanks Claes Ström for the patch.

docs/howto/custom-template-tags.txt

@@ -72,6 +72,8 @@ following:
 
     For more information on the :ttag:`load` tag, read its documentation.
 
+.. _howto-writing-custom-template-filters:
+
 Writing custom template filters
 -------------------------------
 

docs/intro/overview.txt

@@ -16,15 +16,17 @@ Design your model
 =================
 
 Although you can use Django without a database, it comes with an
-object-relational mapper in which you describe your database layout in Python
+`object-relational mapper`_ in which you describe your database layout in Python
 code.
 
+.. _object-relational mapper: http://en.wikipedia.org/wiki/Object-relational_mapping
+
 The :doc:`data-model syntax </topics/db/models>` offers many rich ways of
 representing your models -- so far, it's been solving two years' worth of
 database-schema problems. Here's a quick example, which might be saved in
 the file ``mysite/news/models.py``::
 
-    from django.db import models 
+    from django.db import models
 
     class Reporter(models.Model):
         full_name = models.CharField(max_length=70)
@@ -57,8 +59,9 @@ tables in your database for whichever tables don't already exist.
 Enjoy the free API
 ==================
 
-With that, you've got a free, and rich, :doc:`Python API </topics/db/queries>` to
-access your data. The API is created on the fly, no code generation necessary:
+With that, you've got a free, and rich, :doc:`Python API </topics/db/queries>`
+to access your data. The API is created on the fly, no code generation
+necessary:
 
 .. code-block:: python
 
@@ -135,9 +138,9 @@ A dynamic admin interface: it's not just scaffolding -- it's the whole house
 ============================================================================
 
 Once your models are defined, Django can automatically create a professional,
-production ready :doc:`administrative interface </ref/contrib/admin/index>` -- a Web
-site that lets authenticated users add, change and delete objects. It's as easy
-as registering your model in the admin site::
+production ready :doc:`administrative interface </ref/contrib/admin/index>` --
+a Web site that lets authenticated users add, change and delete objects. It's
+as easy as registering your model in the admin site::
 
     # In models.py...
 
@@ -173,9 +176,9 @@ application. Django encourages beautiful URL design and doesn't put any cruft
 in URLs, like ``.php`` or ``.asp``.
 
 To design URLs for an app, you create a Python module called a :doc:`URLconf
-</topics/http/urls>`. A table of contents for your app, it contains a simple mapping
-between URL patterns and Python callback functions. URLconfs also serve to
-decouple URLs from Python code.
+</topics/http/urls>`. A table of contents for your app, it contains a simple
+mapping between URL patterns and Python callback functions. URLconfs also serve
+to decouple URLs from Python code.
 
 Here's what a URLconf might look like for the ``Reporter``/``Article``
 example above::
@@ -188,7 +191,7 @@ example above::
         (r'^articles/(\d{4})/(\d{2})/(\d+)/$', 'news.views.article_detail'),
     )
 
-The code above maps URLs, as simple regular expressions, to the location of
+The code above maps URLs, as simple `regular expressions`_, to the location of
 Python callback functions ("views"). The regular expressions use parenthesis to
 "capture" values from the URLs. When a user requests a page, Django runs
 through each pattern, in order, and stops at the first one that matches the
@@ -196,6 +199,8 @@ requested URL. (If none of them matches, Django calls a special-case 404 view.)
 This is blazingly fast, because the regular expressions are compiled at load
 time.
 
+.. _regular expressions: http://docs.python.org/2/howto/regex.html
+
 Once one of the regexes matches, Django imports and calls the given view, which
 is a simple Python function. Each view gets passed a request object --
 which contains request metadata -- and the values captured in the regex.
@@ -216,7 +221,7 @@ Generally, a view retrieves data according to the parameters, loads a template
 and renders the template with the retrieved data. Here's an example view for
 ``year_archive`` from above::
 
-    from django.shortcuts import render_to_response 
+    from django.shortcuts import render_to_response
 
     def year_archive(request, year):
         a_list = Article.objects.filter(pub_date__year=year)
@@ -233,8 +238,8 @@ The code above loads the ``news/year_archive.html`` template.
 
 Django has a template search path, which allows you to minimize redundancy among
 templates. In your Django settings, you specify a list of directories to check
-for templates. If a template doesn't exist in the first directory, it checks the
-second, and so on.
+for templates with :setting:`TEMPLATE_DIRS`. If a template doesn't exist in the
+first directory, it checks the second, and so on.
 
 Let's say the ``news/year_archive.html`` template was found. Here's what that
 might look like:
@@ -265,9 +270,10 @@ character). This is called a template filter, and it's a way to filter the value
 of a variable. In this case, the date filter formats a Python datetime object in
 the given format (as found in PHP's date function).
 
-You can chain together as many filters as you'd like. You can write custom
-filters. You can write custom template tags, which run custom Python code behind
-the scenes.
+You can chain together as many filters as you'd like. You can write :ref:`custom
+template filters <howto-writing-custom-template-filters>`. You can write
+:doc:`custom template tags </howto/custom-template-tags>`, which run custom
+Python code behind the scenes.
 
 Finally, Django uses the concept of "template inheritance": That's what the
 ``{% extends "base.html" %}`` does. It means "First load the template called