dsig11 Schema error: NamedCurveType URI use="optional"

from the W3C Working Draft 30 July 2009:

    <complexType name="NamedCurveType">
      <attribute name="URI" type="anyURI"/>
    </complexType>

It should be use="required", shouldn't it?
the missing use-clause suggests it is optional.

IMO, all attributes should have a use-clause.

Cheers
Anders