The iniupdate directory contains a set of scripts that are used to generate the en/appendices/ini.xml table. They also update the information that is dispersed in the en/reference/*/ini.xml files.
To use this script, you must download all the PHP 4, 5 and 6 sources (which will take a long time), so that the script can create a DB with the history of the changes between the versions. To do that, you can just run the ./update-all script. If you are using the 'functable' script as well, you may just create a symlink to its sources, as the sources are the same :) The rest of the process is explained in the README file.
The core of the scripts is in ini_search_lib.php, and it is very regex based. The main regexes work correctly, although some heuristics are used to catch the cfg_get_*() uses. The generate_changelog.php is used to generate the changelog (based on the data previously collected in the DB).
This script requires PHP >= 5 with SQLite.