If you've been poking around the various folders in HTML Purifier,
    you may have noticed the maintenance directory.  Almost
    all of these scripts are devoted to flushing out the various caches
    HTML Purifier uses.  Normal users don't have to worry about this:
    regular library usage is transparent.  However, when doing development
    work on HTML Purifier, you may find you have to flush one of the
    caches.
    As a general rule of thumb, run flush.php whenever you make
    any major changes, or when tests start mysteriously failing.
    In more detail, run this script if:
generate-includes.php)
    generate-schema-cache.php). This usually means
        adding or modifying files in HTMLPurifier/ConfigSchema/schema/,
        although in rare cases modifying HTMLPurifier/ConfigSchema.php
        will also require this.
    HTMLPurifier/HTMLDefinition.php, which also encompasses
        the files in HTMLPurifier/HTMLModule/ as well as if you've
        customizing definitions without
        the cache disabled. (see flush-generation-cache.php)
    generate-standalone.php)
    You can check out the corresponding scripts for more information on what they do.