[whatwg] W3C compatibility

Ian Hickson ian at hixie.ch
Mon Feb 12 14:40:40 PST 2007

On Mon, 12 Feb 2007, James Justin Harrell wrote:
> Will UAs be able to present an API to (X)HTML documents that conforms to 
> both the W3C DOM and the WHATWG's HTML5 DOM?

It isn't always clear what conformance to the W3C DOM means. In practice, 
browsers have in several instances specifically not implemented the W3C 
DOM, because the W3C DOM is not compatible with legacy practice.

The WHATWG DOM explicitly intends to be compatible with existing practice, 
and attempts to be broadly compatible with the parts of the W3C DOM that 
it superseedes. If there are places where this has not been successfully 
done, please let me know.

> 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?

Yes. The XHTML1 specs are so vague about what exactly is required for 
conformance that you could pretty much do anything and still be conformant 
to the XHTML1 specs.

> 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?

No. A better question, though, is whether it would be possible for a UA to 
implement both XHTML2 and XHTML1 in a conforming fashion if they use the 
same namespace.

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

Yes. In fact due to the various different global attributes, every single 
element in XHTML2 can have different semantics than elements with the same 
local name in XHTML5. (e.g. <span href="">, or <span contenteditable="">. 
In addition, a number of elements in XHTML2 and XHTML5 overlap with 
different semantics, e.g. <input>, or with semantics that are defined in 
more detail in XHTML5 than in XHTML2, e.g. <section>, <h1>, etc.

> In each question I'm including all current working drafts but excluding 
> any future work. If there are any incompatibilities, what are they?

There is a wiki page describing some of these differences between HTML4 
and HTML5 (as well as between HTML5 and XHTML):


...but I am not aware of a list of differences between XHTML2 and XHTML5. 
Part of the problem is that XHTML2 defines certain things very vaguely. 
For example, it does not define how to create a table of contents from 
<section>, <h>, and <h1>-<h6> elements, whereas HTML5 does. Would this be 
considered an incompatibility?

In practice, however, this is of less importance than whether a UA will be 
able to implement XHTML1, XHTML2, or XHTML5 while still being compatible 
with existing legacy content on the Web. It is not currently possible to 
fully and conformantly implement XHTML1 while being compatible with the 
Web, nor is it likely to be possible to implement XHTML2 while being 
compatible with the Web if XHTML2 uses the XHTML1 namespace. XHTML5 is 
guarenteed to be compatible with the Web, because if browser vendors find 
any incompatibilities, the XHTML5 specification will be fixed to match.

I hope this answers your questions. There were a number of other e-mails 
on this thread, which I will reply in due course, though not for some 
time. If people want specific e-mails replied to sooner, please let me 

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

More information about the whatwg mailing list