XHTML Role attribute module

This question applies to the XHTML Role Attribute Module draft and to the
corresponding section in the published XHTML 2.0 working draft.

"The ROLE attribute takes as its value one or more white-space-separated
QNames" (section 3).

How should user agents treat a role attribute containing two or more QNames,
the semantics of which, and hence the behaviours associated with which, are
mutually exclusive? This is the case in which the author of the XHTML 
document specifies mutually incompatible roles for the same element.

Informally, I would expect the user agent's implementation of role to operate
somewhat as follows:

1. Taking namespace qualifications into account, obtain the intersection of
the set of roles specified in the value of the ROLE attribute, and the set of
roles recognized by the user agent.

2. Perform whatever processing (in the most general sense of the term) is
associated with each of those roles.

Unless I am mistaken (which is perfectly possible) there is scope for an
interoperability problem to arise when mutually inconsistent roles are
specified: user agents could differ regarding which role is given precedence
in this circumstance.

A simple rule, for example that the first role specified in the value of the
attribute takes priority over later, incompatible roles, would suffice to
address this problem.

Received on Sunday, 19 August 2007 05:51:21 UTC