In section 9.3.2. "Descriptions of many PDLs can be found at http://www.undocprint.org/formats/page_description_languages." 404.
(In reply to freebugs from comment #0) A bunch of the links on that site's left sidebar 404 too. Emailed the listed site maintainer to ask.
(In reply to freebugs from comment #0) > … 9.3.2. … Numbering has changed. Currently 10.3.2 at <https://docs.freebsd.org/en/books/handbook/printing/#print-pdls-summary>.