Caret

[stefnotch]

When one has a row of text, then the caret can be placed inbetween the individual characters.

The same logic applies here. A caret is

• a zipper that points at a row
• an offset, that tells you where in the row the caret is (based on myZipper.value.values.length or myTextZipper.value.value.length)

[stefnotch]

Test cases

1. Try out $\displaystyle \frac{a}{b^{c \color{blue}|\color{black} }}$ where $\color{blue}|$ is the caret and then press up
2. $\displaystyle \frac{2+\sqrt{3_{2\color{blue}|\color{black}}+4}}{0\color{blue}|\color{black}+1\color{blue}|\color{black}+\color{blue}|\color{black}2}$ and place the caret in any of the locations and press up/down

[stefnotch]

Try using ts-pattern in the math-layout-caret code

[stefnotch]

Regarding the caret size w3c/mathml-core#38

[stefnotch]

firefox_2022-11-01-0269.webm

[stefnotch]

A fun case regarding up-down movement. The caret is the thick blue line. When pressing up, where should the caret go?

The 3 options:

1. Before the fraction, because you're moving up into the top part of the fraction. You don't care about nested stuff.
2. After the x^2, because that's the physically closest valid location.
3. Before the y, because you're only moving up a tiny bit.

(For the record: Mathlive does option 1, Mathquill does 2, MathType and MathCha do 3, Guppy does 4, and MathCad doesn't even let you do that)

There's also the alternative option 4:

[stefnotch]

More such cases

[stefnotch]

A sample size of 4 users apparently prefers something like option 4. The absolutely simplest possible thing.

[stefnotch]

Another case: Imagine having typed exactly this and then immediately pressing up

[stefnotch]

Maybe there are papers that go into how a cursor should behave?

[stefnotch]

When clicking on the screen and then computing the closest caret point, remember that carets are lines. So point-line distance.