PHP code to purify and filter HTML

* make HTML markup in text secure and standard-compliant
* process text for use in HTML, XHTML or XML documents
* restrict HTML elements, attributes or URL protocols
using black or white-lists
* balance tags, check element nesting, transform deprecated
attributes and tags, make relative URLs absolute, etc.
* fast, highly customizable, well-documented
* single, 48 kb file
* simple HTML Tidy alternative
* free and licensed under LGPL v3 and GPL v2+
* use to filter, secure and sanitize HTML in blog comments or
forum posts, generate XML-compatible feed items from web-page
excerpts, convert HTML to XHTML, pretty-print HTML, scrape
web-pages, reduce spam, remove XSS code, etc.