<element name="root" xmlns="http://relaxng.org/ns/structure/1.0"> <choice> <element name="child"> <attribute name="type"> <value>Foo</value> </attribute> <!-- Define stuff that's only valid when type is "Foo" --> </element> <element name="child"> <attribute name="type"> <value>Bar</value> </attribute> <!-- Define stuff that's only valid when type is "Bar" --> </element> </choice> </element>