/usr/include/cxxtools/xml/ is in libcxxtools-dev 2.0-4ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/cxxtools/xml/api.h
/usr/include/cxxtools/xml/characters.h
/usr/include/cxxtools/xml/comment.h
/usr/include/cxxtools/xml/doctypedeclaration.h
/usr/include/cxxtools/xml/enddocument.h
/usr/include/cxxtools/xml/endelement.h
/usr/include/cxxtools/xml/entityresolver.h
/usr/include/cxxtools/xml/namespace.h
/usr/include/cxxtools/xml/namespacecontext.h
/usr/include/cxxtools/xml/node.h
/usr/include/cxxtools/xml/processinginstruction.h
/usr/include/cxxtools/xml/startelement.h
/usr/include/cxxtools/xml/xmldeserializer.h
/usr/include/cxxtools/xml/xmlerror.h
/usr/include/cxxtools/xml/xmlreader.h
/usr/include/cxxtools/xml/xmlserializer.h
/usr/include/cxxtools/xml/xmlwriter.h
/usr/include/cxxtools/xmlrpc/api.h
/usr/include/cxxtools/xmlrpc/client.h
/usr/include/cxxtools/xmlrpc/fault.h
/usr/include/cxxtools/xmlrpc/formatter.h
/usr/include/cxxtools/xmlrpc/httpclient.h
/usr/include/cxxtools/xmlrpc/remoteprocedure.h
/usr/include/cxxtools/xmlrpc/responder.h
/usr/include/cxxtools/xmlrpc/result.h
/usr/include/cxxtools/xmlrpc/scanner.h
/usr/include/cxxtools/xmlrpc/service.h