Re: can an attribute prohibited by restriction be added back through a subsequent extension?

The REC says in clause 1.5 of Schema Component Constraint: Derivation
Valid (Extension) [1]:

 Note: This requirement ensures that nothing removed by a restriction
 is subsequently added back by an extension.

That (rather than clause 1.2 as I think Mary was suggesting) is where
the REC tries to answer "no" to the question of "whether an attribute
[or element] removed by restriction could be added back in an
extension."  However the constraint itself, in my view, fails to
achieve this, so processors which allow it are not broken.

I think we should fix this one way or another -- what do you think is
best:

  1) No constraint on re-introduction;
  2) No re-introduction of any kind (apparent intention of current REC);
  3) Re-introduction of unchanged originals only (what the current REC
     actually says)?

ht

[1] http://www.w3.org/TR/xmlschema-1/#cos-ct-extends
-- 
 Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
                     Half-time member of W3C Team
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