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.