For tags, switch from Unicode “letter” to “alphabetic” for allowed characters?

[jotaen]

A “letter” (the allowed character class for tags) is currently defined as “a character from the Unicode Letter category (L)”.

This comment suggests that it would be better to use the “alphabetic” category instead, which appears to be a superset of “letter”.

A brief Google search didn’t yield too much substantial insight into the practical differences between the two categories, so I need to look into this more closely.

[jotaen]

tldr; I’m closing this for now, as I think the current definition is sufficient, especially considering that the “letter” definition is only relevant for tags, but not for any other text.

The Unicode categories are defined as:

• Letter: Lu + Ll + Lt + Lm + Lo
• Alphabetic: Lu + Ll + Lt + Lm + Lo + Other_Lowercase + Other_Uppercase + Nl + Other_Alphabetic

So, “alphabetic” is a superset of “letter”, that adds Other_Lowercase + Other_Uppercase + Nl + Other_Alphabetic:

• Other_Lowercase and Other_Uppercase contains a variety of miscellaneous characters such as roman numerals or letters/numbers with circles around it.
• Letter_Number contains “letterlike numeric characters”, mostly ancient ones, like roman, old persian, cuneiform, etc.
• Other_Alphabetic mostly contains code points from the “non-spacing mark” and “spacing combining marks” categories.

For tags, I’m not sure that any of these additional categories would be useful.