[whatwg] W3C compatibility

[Benjamin Hawkes-Lewis]

James Justin Harrell asked:

> If XHTML2 uses a different namespace from XHTML1, will UAs be able to
> treat XHTML1 documents in a way that conforms to both W3C and WHATWG
> specs?

It's important to clarify whether you mean when serving as text/html or
application/xhtml+xml. W3C explicitly doesn't specify how UAs should
treat XHTML1 served as text/html (Web Applications 1.0 does), which
leaves us with the IETF's suggestion that UAs should copy each other's
error handling. WHATWG is creating a specification for that error
handling.

W3C says all XHTML1 documents must include a DOCTYPE declaration;
"XHTML5"'s DOCTYPE declaration is optional and would be different
anyway. It is not clear to me whether W3C allows DOCTYPE to clarify the
meaning of elements such as <hX> and <abbr>, for which XHTML1 and
"XHTML5" imply different semantics. But UAs could certainly DOCTYPE
sniff in this way. (For an argument against the desirability of doing
so, see http://hsivonen.iki.fi/doctype/, but I still can't see there's
any practical alternative when elements with different semantics share
the same namespace.)

<offtopic>
I think the really interesting question is whether the emergence of free
and open source assistive technology will render /any/ of these new
specs suitable for general use without content negotiation and
transformation for legacy (or lousy) clients. I suspect the answer is
"not fast enough", and that HTML 4.01 Strict will remain the only /safe/
choice for some time. The more we push desktop software developers to
make good use of accessibility frameworks like MSAA and IAccessible2,
the faster this transition can happen, since the less custom code will
be required to accessify each additional application.
</offtopic>

> If XHTML2 ends up using the same namespace as XHTML1, will UAs be able
> to treat XHTML2 documents in a way that conforms to both W3C and
> WHATWG specs? 

Better question: if XHTML2 ends up using the same namespace as XHTML1,
will UAs be able to treat XHTML2 documents in a way that conforms to
both of W3C's own XHTML1 and XHTML2 specs? (I think yes, but again only
with DOCTYPE sniffing.)

> Would there be any overlap, where elements from HTML5 and XHTML 2.0
> with different names perform the same function?

As the drafts stand currently, yes there's plenty of overlap. Examples:

* XHTML2 allows any element to be a link; "XHTML5" does not.

* XHTML2 allows pretty much any element to be included with the src
attribute; "XHTML5" does not.

* XHTML2 and "XHTML5" have wildly different ways of indicating document
structure with headings.

* XHTML2 often uses role attributes to indicate semantics/functionality
where "XHTML5" supplies elements (or uses registered microformats). For
example, XHTML2 defines a role called "note" as "The content is
parenthetic or ancillary to the main content of the resource." "XHTML5"
defines an element <aside/> that "represents a section of a page that
consists of content that is tangentially related to the content around
the aside element, and which could be considered separate from that
content". XHTML2 defines a role called "navigation" for "the navigation
bar on a web document", while "XHTML5" defines a <menu> element.

* XHTML2 uses XForms for forms, "XHTML5" uses Web Forms 2.0.

--
Benjamin Hawkes-Lewis