Added docs about how to create a generic array typecaster

doc/src/extensions.rst

@@ -325,6 +325,20 @@ details.
 
     .. versionadded:: 2.4.3
 
+    .. _cast-array-unknown:
+
+    .. note::
+
+        The function can be used to create a generic array typecaster,
+        returning a list of strings: just use the `~psycopg2.STRING` as base
+        typecaster. For instance, if you want to receive from the database an
+        array of :sql:`macaddr`, each address represented by string, you can
+        use::
+
+            psycopg2.extensions.register_type(
+                psycopg2.extensions.new_array_type(
+                    (1040,), 'MACADDR[]', psycopg2.STRING))
+
 
 .. function:: register_type(obj [, scope])
 

doc/src/faq.rst

@@ -109,6 +109,13 @@ Transferring binary data from PostgreSQL 9.0 doesn't work.
     .. __: http://www.postgresql.org/docs/9.0/static/datatype-binary.html
     .. __: http://www.postgresql.org/docs/9.0/static/runtime-config-client.html#GUC-BYTEA-OUTPUT
 
+Arrays of *TYPE* are not casted to list.
+    Arrays are only casted to list when their oid is known, and an array
+    typecaster is registered for them. If there is no typecaster, the array is
+    returned unparsed from PostgreSQL (e.g. ``{a,b,c}``). It is easy to create
+    a generic arrays typecaster, returning a list of array: an example is
+    provided in the `~psycopg2.extensions.new_array_type()` documentation.
+
 
 Best practices
 --------------

doc/src/usage.rst

@@ -334,6 +334,14 @@ the SQL string that would be sent to the database.
     >>> cur.mogrify("SELECT %s;", ([10, 20, 30], ))
     'SELECT ARRAY[10, 20, 30];'
 
+  .. note::
+
+    Reading back from PostgreSQL, arrays are converted to list of Python
+    objects as expected, but only if the types are known one. Arrays of
+    unknown types are returned as represented by the database (e.g.
+    ``{a,b,c}``). You can easily create a typecaster for :ref:`array of
+    unknown types <cast-array-unknown>`.
+
 .. _adapt-tuple:
 
 .. index::