This is an archived snapshot of W3C's public bugzilla bug tracker, decommissioned in April 2019. Please see the home page for more details.
The DTD for Schemas is missing the optional annotation child of extension. See http://lists.w3.org/Archives/Public/www-xml-schema-comments/2001JulSep/0059.html
Paul also pointed out that the same problem occurs for simpleContent and complexContent. Resolution: The WG agreed that the DTD for Schemas should be modified to include an optional annotation child for extension, simpleContent and complexContent. Erratum item E1-4 has been created.