Validating data-* attributes in XHTML5?

["Graham Hannington" <graham_hannington@fundi.com.au>]

Preamble (if you prefer, skip to the "Question(s)" heading):

I am lagging (years) behind in my knowledge of HTML5 - I have been fixated 
on XHTML 1.0 Strict compliance - but I am trying to catch up.

Someone (thank you, Chris!) recently pointed out to me that HTML5 allows 
attributes named data-* (for example, data-atlassian-layout).

I had observed the use of data-* attributes by various applications, but 
the news of the inclusion of these attributes in the HTML5 spec frankly 
blindsided me (I did say I was far behind).

As mentioned in a recent thread on this mailing list, I have developed a 
DTD and XSDs (W3C XML Schema 1.0) for an XML vocabulary that consists of a 
combination of:
- Proprietary elements and their attributes, and
- Elements that have the same name as elements in XHTML (so far, 
exclusively from XHTML 1.0; and - until now, hence this email - with 
attributes that are a subset of the attributes allowed in XHTML 1.0 
Strict).

This XML vocabulary is evolving. The developers have begun using a 
data-atlassian-layout attribute on div elements.

I have added corresponding explicit definitions for this new attribute to 
the DTD and XSD (for that particular target namespace). But it's raised 
some questions in my mind.

Question(s):

It occurs to me that HTML5 allowing data-* attributes means that any given 
XHTML5 document instance cannot be validated using a fixed, standard XML 
DTD or W3C XML Schema 1.0 (or 1.1, for that matter) document (XSD). 
Because (to my knowledge), DTDs and XSDs require you to explicitly specify 
attribute names; you cannot, in these particular schema languages, define 
attributes with wildcarded names. If an XHTML5 document instance contains 
data-* attributes, then, if you want to use a DTD or an XSD to validate 
it, the DTD or XSD must explicitly define those particular data-* 
attribute names (data-this, data-that; not just data-*). Correct?

Effectively the same point/question, stated slightly differently... With 
XHTML 1.0, one could use a standard DTD/XSD from W3C, unmodified, to 
validate all XHTML 1.0 document instances. It seems to me that you will 
not be able to use a single, standard DTD/XSD from W3C to validate all 
XHTML5 document instances. You'll need to define any data-* attributes. 
Correct?

I imagine that the reaction of many readers will be (a more erudite 
version of) "Well, d'uh! Have you been living under a rock?" I've Googled, 
but have so far not found any rock-solid ;-) answers to this specific 
issue.

Are there any other aspects of XHTML5 that introduce new* problems for 
validating with DTD/XSDs?

* Specifically, compared to validating XHTML 1.0 with DTD/XSDs? (I do not 
seek an answer that covers *all* of the shortcomings of these two schema 
languages - such as the inability to describe various kinds of constraints 
- although I understand that some of these shortcomings are likely to be 
closely tied to the problems with validating XHTML5 versus validating 
XHTML 1.0.)

I am aware of http://html5.validator.nu/ and its associated 
http://about.validator.nu/, and I am learning (for example, about Relax 
NG).

Graham Hannington
Perth, Western Australia

Fundi Software Pty Ltd  2012  ABN 89 009 120 290


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