Dryopteris erythrosora is the Japanese Shield Fern. It also can be used to sanitize HTML to help prevent XSS attacks.
Let's say you run a web site, and you allow people to post HTML snippets.
Let's also say some script-kiddie from Norland posts this to your site, in an effort to swipe some credit cards:
Oooh, that could be bad. Here's how to fix it:
safe_html_snippet = Dryopteris.sanitize(dangerous_html_snippet)
Yeah, it's that easy.
Standing on the Shoulder of Giants
Dryopteris also takes its tag and tag attribute whitelists and its CSS sanitizer directly from HTML5.