1. Run NB [dev feb 05] on fresh userdir $ud (e.g.
/dev/shm/testme) w/ flag
-J-Dorg.netbeans.modules.xml.core.actions=0

2. Make new mount $ud in addition to existing
$ud/sampledir

3. Order $ud above $ud/sampledir

4. Make foo.xml (simple XML doc) in $ud/sampledir

5. Introduce unmatched <bar> element or other
syntax error

6. Run "Check XML"

7. Click on error hyperlink

8. Second copy of foo.xml opened!

9. Close the extra copy of the XML file.

10. Change order again so that $ud below $ud/sampledir

11. Repeat #6 & #7

12. No second copy opened, just focuses original

Problem is in InputOutputReporter.display. (1)
Explicit tricks with file: are bad, use URLMapper.
(2) Converting FileObject -> URL -> File ->
FileObject is lossy.

Suggest for #2 that the XML parser be passed a
special URL, not file:, which encapsulates the
original filesystem. Then no conversion would be
necessary in most cases, unless the user actually
includes a literal file: system ID (as opposed to
relative system IDs). nbfs: is not enough since
relative system IDs might pass outside the mount
point. So make a special URL protocol - you can
declare it globally in the system by adding the
protocol handler to lookup; or just pass it to the
URL constructor. The protocol should encode the
filesystem system name (like nbfs:) followed by
the full file path (like file:); when resolved to
a FileObject, check first on the given filesystem,
only then on other filesystems.

Or pass a file: URL to the parser as now, but also
keep some context indicating the original
FileObject that the action was invoked on. For all
hyperlinks in the output, attempt to resolve them
within that same filesystem if possible - note
that FileUtil.fromFile gives an array, so check
first if any element has the same FS as the
context FileObject, and if not use the first
element arbitrarily.

Also note that log includes some mysterious
exceptions which probably indicate bugs in the code.