xml-escape-string is a compiled Lisp function in ‘xml.el’. (xml-escape-string STRING) Convert STRING into a string containing valid XML character data. Replace occurrences of &<>‘“ in STRING with their default XML entity references (e.g., replace each & with &). XML character data must not contain & or < characters, nor the > character under some circumstances. The XML spec does not impose restriction on ” or ’, but we just substitute for these too (as is permitted by the spec).