Markdown and Textile security

see here Markdown and Textile are two markup languages, that are often used to accept rich text from the user. Usually that works well, especially with another step of sanitization after the conversion. However, sometimes there are bugs in the gems and sometimes the browser accepts strange code:

order cenforce without prescription homograph attack
homograph attack 2
link problems

Redclothérieuse.html Example vulnerability
An older, probably outdated article about Redcloth security