Yes it is an invalid character but clicking on the link in the original post demonstrates that perhaps it should be the browser that filters it out instead of mIRC. No browser I used specifically rejected the URL.
The browser does not filter out the URL as a convenience to the end user so they don't have to type the hex-encoded equivalent. This is also the same reason browsers accept spaces in a URL. By your logic, mIRC should also allow spaces in URLs.
I'll reiterate that people should post their URL's accurately instead of blaming mIRC for it. Given that there are valid characters either side of the > means that mIRC would then have to work harder to process the link the way you want it to.
People are posting their URLs correctly. < and > are specified in the RFC[1] as unsafe because they are used as in-text delimiters for a URL. There are valid characters on either side of a space, too. Why does mIRC stop parsing when it sees a space? The amount of extra work that mIRC would have to do should be negligible. Although, since I can't look at the source code, I can't fairly comment on the complexity or attempt to make a patch for you to use.
I also dispute your claim that posting URLs in a chatroom with < and > added is common. Just because one sees something alot doesn't make it common. I am yet to see any link posted this way in 6 years of IRC.
Just because one doesn't see something alot doesn't make it uncommon. The fact that the Uniform Resource Locator RFC specifically addresses this issue should be reason enough to convince you that this should be fixed.
[1].
http://www.faqs.org/rfcs/rfc1738.htmlTo quote the RFC:
Unsafe:
Characters can be unsafe for a number of reasons. The space
character is unsafe because significant spaces may disappear and
insignificant spaces may be introduced when URLs are transcribed or
typeset or subjected to the treatment of word-processing programs.
The characters "<" and ">" are unsafe because they are used as the
delimiters around URLs in free text; the quote mark (""") is used to
delimit URLs in some systems. The character "#" is unsafe and should
always be encoded because it is used in World Wide Web and in other
systems to delimit a URL from a fragment/anchor identifier that might
follow it. The character "%" is unsafe because it is used for
encodings of other characters. Other characters are unsafe because
gateways and other transport agents are known to sometimes modify
such characters. These characters are "{", "}", "|", "\", "^", "~",
"[", "]", and "`".
