Add docs

lib/sqlalchemy/dialects/postgresql/base.py

@@ -781,6 +781,8 @@ using the ``postgresql_where`` keyword argument::
 
   Index('my_index', my_table.c.id, postgresql_where=my_table.c.value > 10)
 
+.. _postgresql_operator_classes:
+
 Operator Classes
 ^^^^^^^^^^^^^^^^
 

lib/sqlalchemy/dialects/postgresql/ext.py

@@ -171,6 +171,11 @@ class ExcludeConstraint(ColumnCollectionConstraint):
           If set, emit WHERE <predicate> when issuing DDL
           for this constraint.
 
+        :param ops:
+          Optional dictionary.  Used to define operator classes for the
+          elements.
+          See :ref:`_postgresql_operator_classes`
+
         """
         columns = []
         render_exprs = []