[tei-council] Why is <pause> only att.duration.w3c?

[Martin Holmes]

Most timing elements are members of att.duration, which gets them 
att.duration.w3c and att.duration.iso.

But <pause>:

<http://teijenkins.hcmc.uvic.ca/job/TEIP5/lastSuccessfulBuild/artifact/release/doc/tei-p5-doc/en/html/ref-pause.html>

along with its friends in att.timed, is directly a member of 
att.duration.w3c, and not of att.duration.iso:

<http://teijenkins.hcmc.uvic.ca/job/TEIP5/lastSuccessfulBuild/artifact/release/doc/tei-p5-doc/en/html/ref-att.timed.html>

I'm sure there must be a reason that att.timed should be a member only 
of att.duration.w3c and not att.duration, but I can't see it. Anyone know?

Cheers,
Martin