just to add a note on this, the whole idea of inserting "pseudo-markup" into XML text elements seems to be pretty much in disrepute, and certainly caused many complaints about RSS 1.0, see e.g.
http://www.biglist.com/lists/xsl-list/archives/200505/msg00316.html in xsl, you **can** use disable-output-escaping="yes" to convert pseudo-markup to markup, but xslt processors are not required to support this, and so some do not. it sure seems to me that if SOLR is returning XML, it might as well return XML with real markup through and through instead of exploiting pseudo-markup. if there is concern about introducing validation errors, then perhaps you could use namespaces in the XML and put the highlighting markup in a non-SOLR namespace???
