The OASIS XML Catalog document type
The OASIS XML catalog is a document describing a mapping between external entity
references or URI's and locally-cached equivalents. You can read more about using catalogs
in <oXygen/> here.
A file is considered to be an XML Catalog document when it has the following
namespace: urn:oasis:names:tc:entity:xmlns:xml:catalog
or when its root element
name is catalog
.