value-empty is not enough

In [1] John and I took on the action to propose a :value-empty CSS 
pseudo-class.

In reviewing the editor's draft, section G.1 "Pseudo Classes" [2], I've 
been reminded that CSS pseudo-classes are by convention tri-state, so 
for each pseudo-class there should its negation defined as well.   All 
existing Pseudo-classes in G.1 are defined in pairs.  The reason for the 
tri-state is that the middle is not excluded; for example, host language 
elements not bound to instance nodes would be neither empty nor non-empty.

Therefore, I propose that we define :value-empty as a pair, and 
tentatively that we use :value-empty and :value-non-empty.
(There is precedent for the use of hyphenated words; for example, 
:out-of-range and :read-write.)

[1] 
http://lists.w3.org/Archives/Public/public-forms/2008May/att-0054/2008-05-21.html#ACTION3
[2] http://www.w3.org/MarkUp/Forms/specs/XForms1.1/index-all.html#N89852

Leigh.