Using xml as the library name will conflict with other libraries in the realm of Racket, and I neither want to add a prefix typed- to it, hence the sgml/xml. In the future, there would be another sgml/html as well.
Meanwhile, sgml/xml will:
provide a sort of APIs to read and deal with the XML document, with or without tokens information.
provide a Racket language #lang sgml/xml for embedding XML documents in compiled files, as well as hightlighting XML files.