Current version is close to XML 1.0/1.1 compliance, but there are some
features not (yet) fully supported. The main goal of StAX is to make
sure all well-formed documents are parsed succesfully; whether all
problems in other documents are caught is more of nice-to-have
feature.

Known issues regarding strict XML-conformance checking are:

* XML character validity checking:
   * Text content is not checked (except for simple check on NULL char);
     all characters are valid (except for markup).
     Goal will be to do XML 1.1 checking; XML 1.0 character ranges are
     too complicated, without any real benefit. 1.1 fixed most problems.
   * Identifiers are fully checked against XML 1.1 rules; there are no
     plans for strict 1.0 compatibility
   * Additional 2 new XML 1.1 linefeed characters are not recognized as
     linefeeds (and quite likely will not be)
* No verification is done to make sure expanded entities have correct
  nesting; nesting problems will obviously be caught later on if they
  exist after expansion, but strict check to prevent use of "unbalanced"
  elements from entities is not done.
* Checking for recursive entities is done on expansion, not on declaration:
  whether this is allowed by XML specs is not clear.