try {
// XSOM passes the namespace URI to the publicID parameter.
// we do the same here .
InputSource is = opts.entityResolver.resolveEntity(namespaceURI, systemId);
if (is == null) return null;
return new LSInputSAXWrapper(is);
} catch (SAXException e) {
// TODO: is this sufficient?
return null;
} catch (IOException e) {
// TODO: is this sufficient?