XML Schema 1.1 requirements : XML Schema for XML Schema

I would like to submit the requirement for XML Schema for XML
Schema. A markup lanaguage will sometimes need to support data
definitions in XML Schema itself. For example, a business process
markup language (see BPMI.org for BPML) will need to reference XML
Schema types. However, if you want to define a business process markup
language that allows its users to define new XML Schema types inline,
the XML Schema definition for that markup language must reference the
XML Schema definition for XML Schema itself.

In any case, XML Schema is an XML syntax. XML Schema should therefore
be validatable to an XML Schema definition.

Ben