using XML entities to ease adminstration, many SP:s using the same shibboleth2.xml files

[Cantor, Scott]

As a follow up, I can say in regard to what the code is doing, it will
allow resolution of an unregistered (by catalog) resource based on its
systemId if that resource has no embedded slashes, as a local lookup.

So my guess is that in the case in which you made it work, that caused the
parser to ask for a local resource with systemId "foo.dtd" and as long as
that was colocated with the document being parsed, it might load it.

In the other case, whatever you were doing, it must not have resulted in a
resolution of that exact nature.

You can turn up logging on the ParserPool component if you want to get
more feedback on what it's being asked to load.

-- Scott