“extend” an xml schema

[RhitleBet]

I'm trying to "extend" an xml schema (nhibernate here, for example), to add my own entities inside of it.I'm stuck to the point where validation chokes on the "exm:foo" (and exm:foobar) entity, as the "base" schema doesn't allow it. How can I manage to do that, without changing the base schema ?Sample :\[code\]<?xml version="1.0" encoding="utf-8" ?><hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Test" namespace="Test.DataAccess.Entities" xmlns:exm="urn:extend-mappings"> <class name="Post" table="POSTS" xmlns="urn:nhibernate-mapping-2.2" > <exm:foo bar="baz" /> <property name="Body" type="String" column="BODY"> <exm:foobar /> </property> [...] </class></hibernate-mapping>\[/code\]