This is how plugins of type 'factor' are displayed on the "Plugins overview" page:

There are multiple problems with them:

• language string for plugin type is missing (fixed in MDL-78946)
• all standard factor plugins are not marked as standard (fixed in MDL-79238)
• all 'factor' plugins for some reason define dependency on their parent plugin (obviously they can't be installed if the parent is not installed)
• it is impossible to uninstall plugins of this type
• the management link is missing from the plugins overview page
• all version.php files mention 4.2 but this functionality is only available from 4.3 (in fact, I removed this completely)
• no other existing standard plugin defines a 'release', mostly because the versions are bumped automatically by the script but nobody will bother updating releases and they will go out of sync very soon
• one of the standard plugins had MATURITY_ALPHA