Add some internal links.
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index 3f81c00..bc3801a 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -28,7 +28,7 @@
===================== ====================================================================
In addition to the concrete container classes, the collections module provides
-ABCs (abstract base classes) that can be used to test whether a class provides a
+:ref:`abstract-base-classes` that can be used to test whether a class provides a
particular interface, for example, whether it is hashable or a mapping.
.. seealso::
@@ -959,6 +959,7 @@
subclass) or an arbitrary sequence which can be converted into a string using
the built-in :func:`str` function.
+.. _abstract-base-classes:
ABCs - abstract base classes
----------------------------