Observe this question (which will be shortly deleted but is being kept for observation).
So now I'm left to wonder if there is, in fact, another
# question. But should this even be allowed in the first place? I can't think of any legitimate tags that don't include at least one letter or number (404 being an example of a legitimate tag with no letters).
Tagging this question as
Edit: Those tags were stripped out. Which now turns this into a question of, how did that get there?
I was able to add the [#] tag back in by encasing it in double quotes - "#". If you edit this question the quotes are not present in the tags field, however the hash / pound sign is still there.
I also tried to add the other special characters you mention. With all 4 only the dot (.) tag remained. This is what I entered for tags:
bug "#" "." "&" "-"
I can't think of any legitimate tags that don't include at least one letter or number (404 being an example of a legitimate tag with no letters).
It would be awesome to be able to tag things like operators consisting only of symbols
>@> and so on. Especially as Google and most other search engines don't seem to be able to index these tokens. A lot of questions about these operators get repeated over and over, often with a line "I've tried Googling but couldn't find anything".
This feature would actually make me want to use SO's search.
This is my bad -- bug in the sanitization routine. There is a new unrolled loop one now.
The rules for tag strings are somewhat complex:
a-z 0-9 # + - .
-wherever we see it
+is only valid at the end of a tag
*(this is for client side use only; server wildcard is