Untangle fence/zig-zag mess

[Enivex]

• ⦙ was misplaced under fence, presumably because its unicode name is "Dotted Fence". However, I believe this name simply comes from its default math class. It more correctly belongs under dots, even if their math classes are different. It's latex name is \fourvdots
• I renamed fence to zigzag, which is a more descriptive name that's also consistent with their latex naming. (Note that the look of these in New Computer Modern Math is very strange relative to other math fonts.)
• I added the missing ⦚ (class "fence") at the top level of zigzag.

Left to right: zigzag, zigzag.l, zigzag.r, zigzag.l.double, zigzag.r.double, dots.v.quad
Top to bottom: Noto Sans Math, Stix Two Math, New Computer Modern Math.

[MDLC01]

• ⦙ was misplaced under fence, presumably because its unicode name is "Dotted Fence". However, I believe this name simply comes from its default math class. It more correctly belongs under dots, even if their math classes are different. It's latex name is \fourvdots

I strongly disagree with the move of U+2999 ⦙ DOTTED FENCE to dots.v.quad for multiple reasons:

• As you mentioned, the math class is not the same as other variants of dots, indicating different semantics and use cases.
• I don't think anything prescribes that U+2999 specifically consists of four dots.
  • It seems to be four dots in most fonts, but I doubt this is an important characteristic of the character.
• dots.v.quad is probably a better fit for U+205E ⁞ VERTICAL FOUR DOTS.

A possible alternative is dots.v.fence, which focuses on the change of semantics (in a way similar to the existing .big and .op modifiers) rather than on specific glyphs.

• I renamed fence to zigzag, which is a more descriptive name that's also consistent with their latex naming. (Note that the look of these in New Computer Modern Math is very strange relative to other math fonts.)

I like the idea of changing the name to be more descriptive, but I'm not a fan of zigzag. I can think of two issues with that name:

• Its meaning is too restrictive in terms of possible glyphs. As you mentioned, U+29D8, U+29D9, U+29DA, and U+29DB don't look like zigzags in New Computer Modern Math. In fact, only U+299A ⦚ VERTICAL ZIGZAG LINE mentions "zigzag" in its Unicode name (and is is incidentally the only one to look like a zigzag in New Computer Modern Math). The other ones use the term "wiggly fence".
• I personally would intuitively expect zigzag to be lightning bolt-shaped. Actually, we already use the term "zigzag" in arrow.zigzag (U+21AF ↯ DOWNWARD ZIGZAG ARROW), which does look like a lightning bolt.

A possible alternative is wiggle, which solves my first bullet point, but not the second one. Another alternative is bar.v.wiggly, which solves both bullet points, but is very long, and I'm not sure how much it makes sense to fit that under bar. None of those alternatives are satisfying imo.

• I added the missing ⦚ (class "fence") at the top level of zigzag.

Good!

[Enivex]

I'll write more later, but for now I'll just add this

https://www.unicode.org/L2/L2000/00094-n2191.pdf

It specifically specifies "four close dots vertical"

[MDLC01]

Oh that's right. I only looked at the spec and forgot to look at the chart. To link the current one: https://unicode.org/charts/PDF/U2980.pdf

[T0mstone]

The changelog needs to be updated now too (cf. #121 (review)).