Security Like anything that claims to afford security, HTML_Purifier can be circumvented through negligence of people. This class will do its job: no more, no less, and it's up to you to provide it the proper information and proper context to be effective. Things to remember: 1. Character Encoding: UTF-8. Currently, the parser runs under the assumption that it is dealing with UTF-8. Not ISO-8859-1 or Windows-1252, UTF-8. And definitely not "no character encoding explicitly stated" or UTF-7. If you're not using UTF-8 as your character encoding, make sure you configure HTML Purifier or switch to UTF-8. Now. Also, make sure any input is properly converted to UTF-8, or the parser will mangle it badly (though it won't be a security risk if you're outputting it as UTF-8 though). Character encoding is, in general, a knotty issue, but do yourself a favor and learn about it: 2. Doctype: XHTML 1.0 Transitional This is what the parser is outputting. For the most part, it's compatible with HTML 4.01, but XHTML enforces some very nice things that all web developers should use. Regardless, NO DOCTYPE is a NO. Quirks mode has waaaay too many quirks for a little parser to handle. We did not select strict in order to prevent ourselves from being too draconic on users, but this may be configurable in the future. Do you want standards compliance? The doctype is a good place to start. 3. IDs They need to be unique, but without some knowledge of the rest of the document, it's difficult to know what's unique. %Attr.IDBlacklist needs to be set: we may want to consider disallowing IDs by default to save lazy programmers. 4. [PROJECTED] Links We're not going to try for spam protection (although some hooks for such a module might be nice) but we may offer the ability to only accept relative URLs. Pick the one that's right for you. 5. CSS While we can prevent the most flagrant cases from affecting your layout (such as absolutely positioned elements), no amount of code is going to protect your pages from being attacked by garish colors and plain old bad taste. A neat feature would be the ability to define acceptable colors in a document, but that's not likely to be implemented for a while. In the meantime, be sure to make sure that floated elements (permitted, since they can be quite useful) can't mess up your layout. Once again, we may want to disable this by default to protect lazy developers.