Talk:Universally unique identifier

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What are the different variants of Version 4 UUID's used for?

From what I can determine, Version 4 UUID's -- the random kind -- have four variants, signified by the 17th hex digit being one of "8", "9", " a", or "b" (which is how I will refer to each variant here).

What are these four different variants for? How are they used? What determines the use of (say) variant "a" rather than variant "8"?

I'm writing a program to generate these UUID's pseudorandomly, and I don't want to make some kind of ghastly error by providing the wrong type of UUID! Is there a reason why one would use one v4 variant and not another? Are some v4 variants more apprpriate for some uses, and others for other uses? The ONLY document I've yet come across that addresses this issue says (in relevant part):

"...Version-4, variant-1 UUIDs are used in the game Minecraft... Version-4, variant-2 is called a "GUID" on Microsoft systems..." (Source: https://www.uuidtools.com/uuid-versions-explained, Retrieved: Fri., 30-Sep-2022 at 08:43:17pm -0400 UTC.)

However, this leaves unanswered qustions. First (and most obvious) is, what about variants 3 and 4 (what I call "a" and "b" above)?

Also, the phrases "are used in" and "is called a" don't tell me whether these variants are exclusively reserved for these uses, or if it is permitted to use them for other, additional, purposes as well.

The main Wikipedia article doesn't even remotely begin to even touch upon this question...

Guidance? Help? Please?