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Someone created a tag named html+php. How did they do that?

Because the plus sign is interpreted as a tag combination, trying to visit the question list results in all 18,000 questions tagged and .

Using the "edit tag wiki" link on the Tags tab, I was able to get to the tag info page. Unfortunately the trick of viewing the top users page doesn't seem to want to work, as the sole question assigned to the tag doesn't have an answer.

How can we find the question, and how did the user that asked the question manage to create a tag with a plus sign?

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    Lol. I occasionally try to see Meta through an outsider's view. Just looking at the question titles on the front page, they must think we're completely bonkers
    – Pekka
    Jan 17, 2013 at 18:19
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    Are you implying that we aren't?
    – Charles
    Jan 17, 2013 at 18:19
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    @Pekka Now think about what programmers look like to outsiders.
    – user206222
    Jan 17, 2013 at 18:19
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    @whoeverjustdeletedtheircomment, It's on the 10k tools page, under the New Tags header at the bottom. I see one of you just created foo+bar as well.
    – Charles
    Jan 17, 2013 at 18:32
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    It seems like the + character is now allowed by the backend, even though it doesn't work properly. That's that a bug. Maybe it's related to the support of non-English tags.
    – Jeremy
    Jan 17, 2013 at 18:33
  • Hmm, I went to edit the title of the question to reflect the general nature of the bug, and the new tag that @JeremyBanks added gets expanded back out into multiple tags. I was thwarted in recreating a similar tag.
    – Charles
    Jan 17, 2013 at 18:51
  • Oh boy. It's been borked. I think some diamonds and devs are going to be a leetle irritated.... Jan 17, 2013 at 18:53
  • @Charles To recreate this, press enter to submit the form immediately after type the tag name. The JavaScript code that splits it up won't trigger until you type a space or focus on a different input element.
    – Jeremy
    Jan 17, 2013 at 19:15
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1 Answer 1

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Wow, this is an ancient bug.

Like, introduced early August 2009.

The intention with allowing + in tags was for tags like and . This trips against another intention, which is allowing + to be used to separate tags in certain urls.

Looking through the tags that have been created across the Stack exchange network, it looks like the only legitimate use of + has been as a trailing character (as in google+) or as ++ (as in c++11). So those are the rules now, + can only appear in a tag that contains ++ or ends with +.

Changing the url rules would break a ton of urls, so that wasn't really an option.

Those now illegal tags that have already been created will be cleaned up the next time the "unused tag cull" runs, they've already been removed from all posts (which, it turns out, was just this one).

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