An identity constraint's selector and field xpath must be in the XSD 1.0
restricted-XPath subset (Part 1, 3.11.6), far narrower than full XPath: a
leading optional .//, then /-separated steps, a step being '.', a name test
(QName, '*', or NCName:*), or a child:: axis; a field path may end in an
attribute step (@x or attribute::x). No predicates, no other axes, no absolute
or interior //. The xpath was stored raw and compiled lazily with try?, so a
malformed one was silently accepted.
It is now lexed into a whitespace-tolerant token stream and parsed against the
grammar: whitespace between tokens is allowed (child :: a, . //.) while // must
be adjacent and a name test's own ':' may not be spaced. The name lexer uses
the XML NameChar set so a non-ASCII NCName is accepted.
The two identity tests that fed a malformed xpath and expected a
validation-time located error now assert the stronger compile-time rejection.
XSTS: invalid schemas accepted 785 to 736, valid schemas rejected held at 72,
instance buckets unchanged.
