RequestedAttribute/@isRequired "default" boolean value?

A question popped up this week to which replies from my peers were
quite contradictory:

How should RequestedAttribute elements be treated if they lack an
isRequired XML-attribute?  I.e., is there anything suggesting a
default boolean value for isRequired? One interpretation clearly
superior to the other?

So me this always was rather clear, as it's a *requested* attribute
and without adding an explicit isRequired="true" it can only be this,
requsted (not required).
Surprisingly someone else just gave the opposite interpretation, i.e.,
that they understand RequestedAttributes w/o isRequired="false" all as
being strictly required -- which I find very odd.

Would the SSTC care to comment on this matter?

Best regards,
-peter