As expressed in relevant answers here on meta (questions 6808 and 11581) there are URLs which are illegal to use in questions and answers. The system should be enhanced to address those URLs in two ways:
- The editor preview should fail to render them correctly, which it currently does, since this gives the false impression everything would be ok.
- The editor help should be enhanced to warn about illegal URLs, state what is legal and what is not, and advise the user to use alternative URLs (e.g. those obtained by URL shortener services like tinyurl.com etc.), or %-encoding of offending characters, if he needs to use them.