Here is one in C, with flex-generated lexing, for back-end use:

http://www.kylheku.com/cgit/hc/tree/

I used this for allowing HTML in a mailing list e-mails to be incorporated into the web archive. (The archiver is a modified version of Lurker.)

P.S. "wl" stands for "whitelist": what elements are allowed to pass through, and of those, which attributes are allowed to pass through. The condensed "wl" config file is translated into compiled-in static tables by the wl.txr script. No run-time config.