ENTITY declaration

Hi all,

I'd like to create an entity for an XSL element I'm using over and
over again:

<?xml version="1.0"?>
<!DOCTYPE xsl:stylesheet [
<!ENTITY content="<xsl:value-of select='.' />">
]>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="html" indent="yes" />
[...]
</xsl:stylesheet>

I'm using Emacs' nxml mode, and adding this prologue with the entity
declaration immediately invalidates the document.  Also the final '>'
on the ENTITY line isn't highlighted properly, so I must be doing
something horribly worng, but I can't figure out what it is?

TIA

sdt