Add three-valued button about material-ui

[mj12albert]

@sergeyprokhorenko Material UI checkboxes already support 3 states - checked (true), unchecked (false), and indeterminate or mixed (which would correspond to your unknown state)

For the 4th visual state ("all") you are proposing, do you have some more examples of this in the wild? (It could be a simple customization in userland but I'm just thinking out loud)

It could also be addressed by: #38036

[sergeyprokhorenko]

@mj12albert I can't agree with you. See this article: Indeterminate checkboxes are weird

You will never see an individual checkbox in the indeterminate state. But it is the unchecked state that means the absence of any conditions or requirements. The unchecked state means unknown, and not prohibited. Therefore, it is necessary to add a prohibiting state false.

The indeterminate state does not refer to any one individual checkbox. It refers only to a group checkbox and means that the checkboxes in the group can be in any state. I call this state all (states of buttons in the group).

[sergeyprokhorenko]