At Stack Overflow for Japanese (SOja), we can use full-width alphanumeric characters for tags. In Japanese, these characters are used almost the same as their half-width version.


half-width: a
full-width: a

half-width: 1
full-width: 1

At SOja, we prefer to use half-width characters for tags, and the system also tends to support to use half-width tags. In fact, at SOja, a tag written by full-width alphanumeric characters are usually identified with its half-width version. For example, if we move a mouse cursor on a tag [c], it shows a tag description of a tag [c].

A screenshot of a tag description of the full-width c

They, however, are not tag-synonyms. We can still tag a question by a full-width one. Searching by a tag is also treating them as different tags.


Also, it seems that low-rep users can use a full-width tag if its half-width version exists. For this reason, it often happens that full-width tags are used wrongly.

Currently, SOja users correct these tags by hand, which is time-consuming. Related issues were post to SOja Meta in the past (1, 2), but a SOja manager at that time said "This is difficult to fix. The root cause of this problem is the difference of character handling between SQL and C#".

But it is troublesome to check all tags and detect full-width characters manually. Is it possible to avoid creation of tags with full-width alphanumeric characters? For example, can we restrict these characters (say, U+FF01...U+FF5E) for tags? Or, can we treat them as half-width characters like tag synonyms?

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    How extensive is this? Can these full width characters only be used on SOja, on international sites, or can they be used for tags any Stack Exchange site? – 1201ProgramAlarm Feb 12 '20 at 2:08
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    @1201ProgramAlarm Nice comment. I also want to know that. I cannot fully confirm that due to my low reputation at other sites. At least I confirmed that I cannot tag a question with full-witdh [c] at SOen on the question creation page /questions/ask, but can tag at SOes. – nekketsuuu Feb 12 '20 at 3:22
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    I made a quick edit to test, and while it allowed me to create a tag named testingg, it didn't allow that for tesuto. So maybe this is only enabled on SOja (+ possibly other international sites). – muru Feb 12 '20 at 3:27
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    I admit to not being an expert in typesetting but I wouldn't even now how to make full vs half width characters... and I don't even know what the characters I type with are... so that kinda argues that maybe it's not even a thing people think about in English? – Catija Feb 12 '20 at 3:47
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    @Catija English = halfwidth, I believe. To type in fullwidth usually you'd use an IME to convert keyboard input into a different character set. example – Rubiksmoose Feb 12 '20 at 3:56
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    Also at Chinese.SE, e.g. . – Rebecca J. Stones Feb 12 '20 at 4:50
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    O r j u s t t y p e a s p a c e i n b e t w e e n e a c h c h a r a c t e r t o s e e h o w r e d i c u l o u s t h i s l o o k s. – Luuklag Feb 12 '20 at 8:23
  • And then the comment editor removed all my doubled up spaces... – Luuklag Feb 12 '20 at 8:23
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    @Luuklag No, full-width alphanumeric characters are commonly used in order to make typographic harmony with Japanese Hiragana/Katakana/Kanji, which are full-width by default. So they are not margined half-width characters, but characters designed for the special purpose. Here, we SOja users want to use half-width characters for a tag name because it often contains English words. – nekketsuuu Feb 12 '20 at 8:34

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