[userbinator]

I usually remove trailing spaces from URLs, and a lot of auto-linkifying processes (if they're Unicode-aware) will likely strip them too, so I predict this method won't be robust enough to survive a lot of the handling that URLs are often subject to.

If I'm filling out some form fields with URLs, I strip trailing (and leading) spaces too.

[onion2k]

These are zero width characters. There's no reason why they have to be at the end of the URL.