Re: C.4 Undeclared entities?

> I think you're missing Charles' point: that one goal is for XML documents
> to *also* be SGML documents.  To do that, they *must* have at least
> "<!DOCTYPE typename SYSTEM>" at their start.

They must also have a DTD to be valid SGML documents.

> Note that any *existing* SGML processor can consider this to be valid by
> defining its algorithm for resolving the omitted SYSTEM identifier to be
> "parse the document

Please name any existing SGML processor that works this way today.
If you have to change the code, you're not talking about an
existing parser.

A modified parser could just as easily insert a DOCTYPE line.