I think the "target/p2artifacts.xml" and "target/p2content.xml" files
are generated by Maven. They are well-formed XML but Eclipse's XML
validator legitimately warns that they lack grammar constraints.
Since we're not maintaining the tool that creates these files, we are
not in a position to do anything about that. Therefore, we may as
well exclude these from validation entirely. That way we can
more-clearly recognize warnings that we *can* do something about.
In theory, these files could be checked against the DTD given at
<http://help.eclipse.org/neon/index.jsp?topic=%2Forg.eclipse.platform.doc.isv%2Freference%2Fmisc%2Ffeature_manifest.html>.
In practice, Eclipse's structured editor for this file type discards
any "<!DOCTYPE ...>" declarations one might manually add. So there's
no convenient way to tell Eclipse' XML validator what grammar to use.
Fortunately, that same structured editor makes it unlikely that anyone
will introduce invalid content. So I don't mind excluding these files
from XML validation entirely.
Eclipse validation warns about invalid HTML content in all
Maven-generated "target/site/dependency-convergence.html" files. The
warnings are legitimate: these HTML files are indeed invalid.
However, we don't maintain the tool that generates these files, so we
are not in a position to fix them. Better, therefore, to suppress
these warnings so that we can notice and fix other problems over which
we do have control.
Ben Liblit