Fixed #24938 -- Added PostgreSQL trigram support.

docs/ref/contrib/postgres/lookups.txt

@@ -2,6 +2,32 @@
 PostgreSQL specific lookups
 ===========================
 
+Trigram similarity
+==================
+
+.. fieldlookup:: trigram_similar
+
+.. versionadded:: 1.10
+
+The ``trigram_similar`` lookup allows you to perform trigram lookups,
+measuring the number of trigrams (three consecutive characters) shared, using a
+dedicated PostgreSQL extension. A trigram lookup is given an expression and
+returns results that have a similarity measurement greater than the current
+similarity threshold.
+
+To use it, add ``'django.contrib.postgres'`` in your :setting:`INSTALLED_APPS`
+and activate the `pg_trgm extension
+<http://www.postgresql.org/docs/current/interactive/pgtrgm.html>`_ on
+PostgreSQL. You can install the extension using the
+:class:`~django.contrib.postgres.operations.TrigramExtension` migration
+operation.
+
+The ``trigram_similar`` lookup can be used on
+:class:`~django.db.models.CharField` and :class:`~django.db.models.TextField`::
+
+    >>> City.objects.filter(name__trigram_similar="Middlesborough")
+    ['<City: Middlesbrough>']
+
 ``Unaccent``
 ============