No < in Attribute Values

In reviewing a test case, I discovered there was some confusion about
this WFC:

  Well-formedness constraint: No < in Attribute Values

  The replacement text of any entity referred to directly or
  indirectly in an attribute value MUST NOT contain a <.

The person who wrote the test case concluded that this WFC made the
following document not well-formed:

<!DOCTYPE foo [
<!ENTITY x "&lt;">
<foo attr="&x;"/>

I wonder if there's somewhere else in the spec that makes this clear,
or if we want to consider an editorial clarification.

                                        Be seeing you,
                                          norm

-- 
Norman Walsh
XML Standards Architect
Sun Microsystems, Inc.