Signature validity / schema avoidance (ODF 1.2 Part 3 Draft 12)

Dear all,

The dsig schema contains the following comment

<!-- To avoid inclusion of the complete XMLDSIG schema, anything -->
<!-- is allowed within a xmldsig:Signature element               -->

Why is "avoiding inclusion" a goal?

Nowhere is it stated that the content of these subtrees must be valid to
the W3C schema.

- Alex.