For the SYSTEM
identifier for XHTML 1.0 Transitional as recommended by Strictly Conforming Documents
the server reply is
Vary: negotiate, User-Agent
And when you try the content location explicitly, you
Therefore, XHTML documents with the recommended
DOCTYPE do not validate as XML. This misconfiguration is a severe bug and it
may cause major disruption to XML applications worldwide.
links in Document
Type Definitions work,
are free to use any
SYSTEM identifier that works, although it is not recommended.
Note that all DTDs refer to the invalid location in
the usage section.
Why are the DTDs served as text/plain?
They should be served as application/sgml and application/xml-dtd,