Hi, I find that a regualr expression below let $regex := 'P{Ll}' let $input := .//subsection[matches(@title,$regex)] causes the error [FORX0004] Regular expression: 'Lexical error at line 1, column 3. Encountered: "L" (76), after : "{"'. I use P{Ll} in xslt/xpath in saxon without issue and I'm running basex with saxon so I assume this is something basex is parsing out as an error condition I looked in the xquery spec for the error and found which seems to be something else An error is raised [err:FORX0004<http://www.w3.org/TR/xpath-functions-30/#ERRFORX0004>] if the value of $replacement contains a "$" character that is not immediately followed by a digit 0-9 and not immediately preceded by a "\". Let me know your thoughts Regards -- - Alex G. Muir Software Engineering Consultant Linkedin Profile : http://ca.linkedin.com/pub/alex-muir/36/ab7/125 Love African Kora Music? Take a moment to listen to Gambia's Amadu Diabarte & Jali Bakary Konteh www.bafila.bandcamp.com your support keeps Africa's griot tradition alive... Cheers!