Tri-state Checkbox - #14611

[triState] and [value] on the last line

[tryState]

I would probably spell this "tristate", since "tri" isn't a word, but a prefix.

[onChanged]

[value]

not sure what you mean by "applied to" in this paragraph

https://en.wikipedia.org/wiki/Apply

Ah, ok. I think that phrasing would be confusing to our less mathematically-inclined users. I'd probably just say "will be called with the value" or some such.

not sure what "applied to" means here either

https://en.wikipedia.org/wiki/Apply

nit: missing newline after last argument

[triState]

[triState], [value]

[triState], [value]

we need to convey the null state to the accessibility system

I'd like to defer that to a separate PR. I've discussed it with @goderbauer; support for tristates isn't trivial.

Can you leave a TODO here and/or file a bug?

In general we should have the rule that all new widgets support accessibility, text scaling, localization, and bidi out of the box, but if there's a reason to make an exception here then ok.

Added a TODO and filed #14677

if tristate is true, this doesn't seem to give the user a way to get back to the indeterminate state. It seems like if tristate is true, this should go in the loop false -> true -> indeterminate -> false.

That was intentional however I see that HTML tristates do cycle this way. So we can too.

The main reason to do it this way is that if someone doesn't want this behaviour, they can easily just set tristate to false once the value isn't null, but if they do want this behaviour, there's nothing they can do if we don't implement it by default.

this should verify that animations correctly handle:

true -> false
true -> indeterminate
false -> true
false -> indeterminate
indeterminate -> true
indeterminate -> false