SchemaEntityRefType#isContainer.

[Gary P Cole <Gary.P.Cole@Sun.COM>]

The optional attribute #isContainer of SchemaEntityRefType should have a 
default value. 

I believe that #isContainer should default to "false" (and the spec is 
written that way), but even a default of "true" seems better than no 
default at all.  A default value makes the absence of this optional 
attribute less ambiguous.

If we cannot agree on a default value, then let's *require* the 
attribute.  This is also unambiguous.

Gary