flex-old-doc 2.5.4a-10.1 (amd64 binary) in ubuntu jammy

 This package contains the HTML documentation for the old 2.5.4a version
 of flex, which is no longer being developed upstream. You should
 normally chose flex-doc, unless you have legacy lexer files that do
 not work with a modern flex, and need to use the old flex. The
 upstream source code can be found at the FTP site:
 http://flex.sourceforge.net/