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I came across this weird tag accidentally. SO claims there are 67488 questions tagged with it. Is it a bug or a feature?

The screenshot:

enter image description here

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Seems to be gone now. – Tim Post Feb 8 '12 at 15:32
@TimPost Hm. I'm still seeing the thing on the Questions page in Related Tags. – Costique Feb 8 '12 at 15:43
I see 2,626,020 questions tagged...o.O – tombull89 Feb 8 '12 at 15:47
Another weird thing is that I cannot find the tag using search or filtering the Tags page. – Costique Feb 8 '12 at 15:49
Possible duplicate:… – Costique Feb 8 '12 at 15:57
@Costique Yup, but I'm not inclined to close this, as this seems to be one of those bugs. Ya know, the kind that has been linked to Tourette Syndrome. – Tim Post Feb 8 '12 at 16:01
@TimPost: I'm seeing this in my list as well... – animuson Feb 8 '12 at 17:15
This is strange, I can't reproduce it. – Tim Post Feb 8 '12 at 17:17
@TimPost It's still there for me, though. Its number of questions is fluctuating as if it's a real thing. – Costique Feb 8 '12 at 17:21
Wait, reproduced, look at the related tags between SQL and Ruby On Rails (thanks @Fabian) – Tim Post Feb 8 '12 at 17:22
@TimPost: I also notice that specific tag has a title="show questions tagged '*~294'" whereas all the other tags in that list have a title=""... – animuson Feb 8 '12 at 17:25
@TimPost Yay! That's it. I wonder if there's a valid tag which has the exact same number of questions. Could a valid tag be renamed/aliased? – Costique Feb 8 '12 at 17:31
Also found in the Tagged Questions for c++, which shows *~294 × 12836. – kennytm Feb 8 '12 at 19:58
up vote 17 down vote accepted

We had a secret sub-domain that we used to test features required for and recently removed it.

This tag is just some stale data that will be purged in a few hours, after peak traffic.

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And you would have gotten away with it, if it weren't for us meddling kids! – Tim Post Feb 8 '12 at 20:15
shakes fist angrily – Jarrod Dixon Feb 8 '12 at 20:16
Thanks for fixing it. Yeah, Facebook is evil, it's that bad. – Costique Feb 9 '12 at 4:34

I can't say why the tag was appearing in that list, but it seems to be a valid combination of wildcards. The * character is a client-side wildcard and ~ is a server side wildcard. The server-side wildcard has the additional restriction that you need at least 4 characters in your pattern or it will be rejected.

So what this tag pattern means is

*   :match anything client-side
~   :match anything server-side
294 :match 294

The last match is needed because of the server-side 4 character limit, if you remove the last character the pattern is rejected. If you use a number there that doesn't exist in any tag this part seems to be ignored entirely and you're left with a pattern that matches every question on the site.

For tag the client-side wildcard is automatically replaced by the server-side wildcard, so this pattern is equivalent to ~~294.

That this URL works is probably a feature, but this tag certainly shouldn't appear in any tag listings.

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Thanks for the explanation. Looks like a bug. I wonder where the number comes from. – Costique Feb 8 '12 at 15:55

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