BTW - I highlighted HTMLPurifier on my blog again. I'm using it to filter blog posts before database storage (mainly since the idea of leaving potential XSS in the database and using post-filtering for display bothered me - what if I migrate the posts to another application without HTMLPurifier? Meh!).
I'll keep on highlighting it too. Truly excellent library.
I usually just use the actual Constant name itself if possible. I was watching Placeholder's in the ZF, and to use a constant I had the option of Zend_View_Helper_Placeholder_Container_Abstract::PREPEND or "PREPEND". I'll leave it others to guess which I'm usingI just figured it's easy to read, but yeah the increments are larger than they need to be.