[syslog-ng] XML entities in PatternDB

I'm trying to find a way to use non-printable characters to delimit messages to avoid problems with escaping message delimiters. However, I'm having trouble representing any special characters in the patterndb.xml file. Specifically, I'd like to use characters like those found here: http://en.wikipedia.org/wiki/List_of_XML_and_HTML_character_entity_reference... as U+200C. Trying to use the XML entity name, ‌ results in an error: "Entity name \'zwnj\' is not known." Is there a place that lists what entities are allowed in the XML? Thanks, Martin