JUnit 4 XML schematized?

There's a pretty standard format for JUnit XML output.  You've
probably seen it: there's a <testsuite> root element containing
zero-or-more <testcase> elements, each of which may contain a
<failure> or <error> element.  (There's also a <properties> element
with zero-or-more <property> elements.)  A lot of tools know how to
read this format and report on it, including at least Ant, Maven,
Cruise Control, Hudson, Bamboo, Eclipse and IntelliJ IDEA.

Is this XML standardized anywhere in a DTD or XML Schema or something?

If there isn't a standard, could we go about making a standard and
blessing it?  (Perhaps JUnit 4.5 could include an XMLReporter that
could be a reference implementation.)

In particular, I'm curious to know how one would represent that a test
has been ignored in "standard" JUnit XML.

-Dan