Add \ion, \positiveion, \negativeion commands for chemistry notation

[drdrew42]

What

Adds three LaTeX commands for chemistry ion-charge notation:

• \ion[sign]{charge} — a superscript-only command: an editable charge block followed by a fixed +/- sign, rendering e.g. the "2+" of a 2+ cation.
• \positiveion / \negativeion — sign-bound shorthands that canonicalize to \ion[+]{…} / \ion[-]{…}.

Why

These commands existed in a downstream MathQuill fork used for WeBWorK chemistry problems — the chemistry answer-entry toolbars drive \positiveion/\negativeion for entering ion charges. They were lost when that work moved onto @openwebwork/mathquill, silently breaking those toolbar buttons. Restoring them upstream lets the downstream work drop the private fork.

How

Ion extends SupSub, mirroring the existing subscript/superscript classes in commands.ts — supsub = 'sup', an htmlTemplate carrying the editable charge block plus a .mq-ion-classed sign span, and a parser() built on latexMathParser.optBlock / .block exactly like NthRoot. latex() serializes to \ion[sign]{charge}; an absent optional sign defaults to +, and an empty charge block to 1.

.mq-ion is a styling hook on the sign span — no CSS rule is added; it renders correctly with the existing mq-sup styles.

Testing

• npm run build, npm run lint:check, and npm run format:check all pass.
• Round-trip parse tests added to test/latex.test.ts (the ion charges test), following the existing assertParsesLatex pattern.

🤖 Generated with Claude Code

[drgrice1]

I think you need to add some explanation of how to use this, and how this would work with PG. This isn't something that can be directly typed into a MathQuill input.

[drdrew42]

Originally, LibreTexts wanted to implement a toolbar for chemistry problems (see repo for foundations), and looped in Davide to help improve contextReaction.pl (which includes implementation of ions, compatible with this extension of MathQuill)... and some of that work has now been folded into PG official.

They're finally pulled up to date with PG, but that migration has hit a snag -- as it seems I never submitted the ions implementation to our fork of MathQuill.

Ions are not "real" LaTeX, and it is unexpected that any student would type them in (though they could...), rather it is expected that mathquill toolbar entries be added for them (LibreTexts has macros for this already):

{ 	id: 'positiveion',
	latex: '\\positiveion',
	tooltip: 'postitive ion',
	icon: '\\text{ }^{\\text{ }+}' 
},
{ 	id: 'negativeion',
	latex: '\\negativeion',
	tooltip: 'negative ion',
	icon: '\\text{ }^{\\text{ }-}' 
},

I have a similar request to add a \sci command -- enabling the toolbar-triggering of a scientific notation entry (which I can extend on this PR, or file separately). Clearly students can individually enter the multiplication, base 10, and exponent -- but there is no way for the toolbar to facilitate a "combo move" like this without a dedicated command. Or maybe I've missed something?

[drgrice1]

Now that the toolbar is part of this repository, you should merge in the main branch to get it and demonstrate the usage, or how to implement a toolbar button. Currently with this pull request I am not able to get anything to work with the toolbar.

[drdrew42]

Sorry, I had the triple-layer escaping going there, only need the double for input-test.js

I had no problems adding the following to input-test.js

mathField.options.addToolbarButtons([                                                                                                                                                                                                                                                
    { id: 'sci', latex: '\\sci', tooltip: 'scientific notation', icon: '\\times10^\\text{ }' },                                                                                                                                                                                        
    { id: 'positiveion', latex: '\\positiveion', tooltip: 'positive ion', icon: '\\text{ }^{\\text{ }+}' },                                                                                                                                                                            
    { id: 'negativeion', latex: '\\negativeion', tooltip: 'negative ion', icon: '\\text{ }^{\\text{ }-}' }                                                                                                                                                                             
]);                                                                                                                                                                                                                                                                                  

Well, I say no problems -- there's some issue with the appearance of the icons, I'm working on that. With the ions, it's a matter of combining whitespace with another glyph...

1. Do you want these buttons actually added to input-test.js in this PR?
2. Do you want me to fix the whitespace+glyph spacing?

[drgrice1]

No, I think those buttons shouldn't be added to the input-test.html file. I only added the subscript button to demonstrate the way to add buttons.

I figured out how to use this. What was confusing me was that since these define from SupSubs the supSubsRequireOperand applies. So something needs to be typed first to use these.

One thing that is going to be needed for these is mathspeak.

[drdrew42]

Okay, I've added mathspeak for \sci and the ions. But in writing the corresponding tests, I found that the unit-test.html wasn't running the suite -- so I added that fix as a follow-up commit.