Hi Gerrit, Right, the »parameter-document« serialization parameter is currently not supported by RESTXQ, as this might cause too many conflicts at runtime. You can try »use-character-maps« instead (with and without RESTXQ, with a slightly non-standard syntax): declare %rest:path("/test") %output:use-character-maps(">=>,1=3") function _:html() { <xml> 1 > 2 </xml> }; declare option output:use-character-maps '>=>,1=3'; <script> 1 > 2 </script> serialize(<xml> 1 > 2 </xml>, map { 'use-character-maps': '>=>,1=3' } ) …and the standard way, for fn:serialize, as a reminder: serialize(<xml> 1 > 2 </xml>, map { 'use-character-maps': map { '>': '>', '1': '3' } } ) Keys and values are separated by the equal sign; pairs are separated by commas. Separators that are to be defined as keys or values can be encoded as entities (see the updated article on serialization parameters [1]). Hope this helps, Christian [1] https://docs.basex.org/wiki/Serialization#Parameters