When I tried to parse my XHTML Strict files with DOM extension, it couldn't understand xhtml entities (like ©). I found post about it here (14-Jul-2005 09:05) which adviced to add resolveExternals = true, but it was very slow. There was some small note about xml catalogs but without any glue. Here it is:

XML catalogs is something like cache. Download all needed dtd's to /etc/xml, edit file /etc/xml/catalog and add this line: <public publicId="-//W3C//DTD XHTML 1.0 Strict//EN" uri="file:///etc/xml/xhtml1-strict.dtd" />

Thats all. Thanks to http://www.whump.com/moreLikeThis/link/03815