Over-riding Native Semantics (seeking clarification)

Greetings ARIA WG,

Recently, I was made aware of two claims made in the ARIA 1.1 specification
which caused me to question the statements. Specifically, the current spec,
when speaking about *aria-rowspan* and *aria-colspan*, states:

If aria-rowspan is used on an element for which the host language provides
an equivalent attribute, user agents
<https://www.w3.org/TR/wai-aria-1.1/#dfn-user-agent> *MUST* ignore the value
of aria-rowspan and instead expose the value of the host language's
attribute to assistive technologies
<https://www.w3.org/TR/wai-aria-1.1/#dfn-assistive-technology>.

(Note: I am quoting the aria-rowspan text, but it states the same for
aria-colspan as well)

Is there an explanation/reason why these two attributes operate differently
than most aria attributes & values, which normally over-ride Native
Semantics? I must confess I was surprised when I was pointed to this
discrepancy regarding ARIA's semantics in these cases, up to and including
questioning whether this is an editorial misunderstanding.

Thanks in advance for any clarity the WG can provide.

JF



-- 
*John Foliot* | Principal Accessibility Strategist | W3C AC Representative
Deque Systems - Accessibility for Good
deque.com