XSLT and XHTML DTD's
<xsl:output method="xml" encoding="utf-8" omit-xml-declaration="yes" indent="no" doctype-system="http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd" doctype-public="-//W3C//DTD XHTML 1.0 Strict//EN" />
Another tidbit I found today was:
exclude-result-prefixes="media"
to exclude unwanted namespace declarations from the output.