[whatwg] External document subset support

[Brett Zamir]

Section 10.1, "Writing XHTML documents" observes: "According to the XML 
specification, XML processors are not guaranteed to process the external 
DTD subset referenced in the DOCTYPE."

While this is true, since no doubt the majority of web browsers are 
already able to process external stylesheets or scripts, might the very 
useful feature of external entity files, be employed by XHTML 5 as a 
stricter subset of XML (similar to how XML Namespaces re-annexed the 
colon character) in order to allow this useful feature to work for XHTML 
(to have access to HTML entities or other useful entities for one, as 
well as enable a poor man's localization, etc.)?

If you wish to give power to the average user (as well as perhaps, as a 
side effect, encourage implementation of parsing mechanisms for pure XML 
over the web which enable the many "non-web" textual documents out there 
which already use external DTDs to be shared and styled over the web), I 
believe requiring support for (non-validating) external DTD subsets 
would provide a very useful feature to many web users, regardless of the 
laxity of the original XML specification on this matter.

While some might argue that causing a fatal error in XML parsers will be 
unacceptable, use of a colon in an XML name, while technically allowable 
by XML, will also produce such a fatal error in latter (namespace-aware) 
parsers. While some XML parsers might not yet support external DTD 
parsing, I would hope that the bar could be raised higher with a new 
version of XHTML, especially if new features are being introduced 
anyways, and especially given all of the benefits this could bring to 
both XHTML as well indirectly to XML users. True XHTML is still more of 
an experimental field anyways, so I don't think the world will collapse 
if an old XML parser breaks on visiting such a page (HTML will still be 
fine), while failing to allow it now may delay or prevent future XML 
parsers from ever supporting this very reasonable functionality.

thank you,
Brett Zamir