An object that implements this interface that can be called by the processor
to turn a URI used in document(), xsl:import, or xsl:include into a Source object.
Called by the processor when it encounters
an xsl:include, xsl:import, or document() function.paramhref An href attribute, which may be relative or absolute.parambase The base URI against which the first argument will be made
absolute if the absolute URI is required.returnA Source object, or null if the href cannot be resolved,
and the processor should try to resolve the URI itself.throwsTransformerException if an error occurs when trying to
resolve the URI.