[relax-ng] Enabling validation for RNG

I mentioned this at the last telcon, but I thought I'd get the idea
on record:

A mode of validation analogous to feasible validation, in which a document
counts as valid iff it can be made so by removing arbitrary amounts of
elements, attributes, and/or text.  I think of this as "interleaving
with any", but it may not be directly implementable as such due to
restrictions on interleave.

It is closely related to the SGML/AF notion of "enabling validation" as
defined at http://www.ornl.gov/sgml/wg8/docs/n1920/html/clause-A.3.1.html .

-- 
John Cowan       http://www.ccil.org/~cowan        <>
        You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
        You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
                Clear all so!  `Tis a Jute.... (Finnegans Wake 16.5)