XML schema location files offer a way to locate the schema for a
XML-document. They have been defined by XML-Guru James Clark (as apart
of his nXML-Emacs mode).
As James wrote: "Unlike DTDs, RELAX NG does not specify a way to
locate the schema for a document. nXML mode's way is to use a list of
schema locating files. A schema locating file is an XML document
specifying rules for locating a schema. It must be valid with respect
to the schema locate.rnc. Each file specifies a list of rules. The
rules from each file are appended in order. To locate a schema each
rule is applied in turn until a rule matches. The matching rule is
then used to determine the schema."
Now what's needed is a tool to manipulate these schema location files,
something like 'xmlcatalog' is for DTD catalogs. This is what