Invisible operators

[MDLC01]

Context

Unicode defines multiple invisible operators, which are meant to disambiguate juxtaposition in mathematical text. This is primarily destined to be used by symbolic calculation softwares and screen readers. Their use is not mandatory but recommended to improve accessibility.

Invisible operators are the topic of section 2.14 of UTR #25 (the Technical Report on Unicode Support for Mathematics), and section 22.6 of the more recent, and authoritative Unicode 16.0.0 Core Specification.

Invisible operators were previously mentioned in typst/typst#721 (comment).

Formal proposal

Add the symbol variants from the following table under sym.

Character	Name
U+2061 FUNCTION APPLICATION (Binary)	???1
U+2062 INVISIBLE TIMES (Binary)	times.invisible
U+2063 INVISIBLE SEPARATOR (Punctuation)	comma.invisible2
U+2024 INVISIBL PLUS (Special)	plus.invisible

Alternative names

Other possible names include invisible.{application,times,comma,plus}.

Concerns

Invisible operators seem to not be handled properly by the default math font.

Footnotes

1. TODO: Find a name. ↩

2. U+2063 has the Unicode informative alias "invisible comma." ↩

[T0mstone]

How about invis instead of invisible? Seems nicer and still totally unambiguous.

[MDLC01]

This is another option indeed, although I personally tend to prefer full names.

[Enivex]

Maybe they should all be under invisible instead, considering how special they are?

For the same reason I think the long name makes sense. This isn't something most people will use in a non-programmatic way

[T0mstone]

Hm, probably true, though it makes more sense semantically to have them as variants of the operators they are.

[samimaat]

I can confirm that the invisible operators are definitely used by screen readers (as opposed 'presumably' in the first post).

MathCAT is an addon to NVDA (an open source screen reader). It will also be implemented to NVDA in the future. This is also true for JAWS, which is another screen reader. MathCAT intereprets the invisible operators.

Great that the invisible operator input and output would be supported!