PR#46582 document that modules can implement internal map functions

minor changes to original due to changes in context.

Submitted by: Bob Ionescu
Reviewed By: Eric Covener


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@1031347 13f79535-47bb-0310-9956-ffa450edef68