- http://xmlstar.sourceforge.net/doc/UG/xmlstarlet-ug.html
- http://www-106.ibm.com/developerworks/xml/library/x-matters17.html – does no longer work as of 2017-10-02 (probably quite a little earlier already)
- http://www.ibm.com/developerworks/xml/library/x-matters17.html – does no longer work as of 2021-08-31 (probably quite a little earlier already)
- https://www.ibm.com/developerworks/xml/library/x-matters17/x-matters17-pdf.pdf – this is the actual and relevant document (broken link as of 2021-08-31)
- https://duckduckgo.com/?q=xml+pyx