Using Python and lxml to validate a third-party XSD, I get the following error already while parsing the FB2 (FictionBook) schema:
lxml.etree.XMLSchemaParseError: attribute use (unknown),
attribute 'ref': The QName value
'{http://www.w3.org/XML/1998/namespace}lang'
does not resolve to a(n) attribute declaration., line 52
The schema part responsible to this error looks like the following:
<xs:attribute ref="xml:lang"/>
In fact, FB2 is a well known format, so I can't imagine the schema really has an error; rather my parser has a wrong setting?
Here is my code following a working example from the lxml manual.
f = StringIO(file_to_string("data/spec/FictionBook.xsd"))
xmlschema_doc = etree.parse(f)
xmlschema = etree.XMLSchema(xmlschema_doc)
