Would it be possible to extend the TWebCheckBox with a property AllowGrayed like in the VCL checkbox?
TWebCheckBox maps on a HTML INPUT element with type "checkbox" and this isn't offering a grayed state. So, it is only possible by creating a custom checkbox control.
A possible way could be to integrate one from
https://uiverse.io/elements?search=checkbox&page=1
with the help of what is explained in:
And what about the HTML input's indeterminate property? Doesn't it reflect the grayed state?
There was a reason we couldn't use it when we implemented it a couple of years ago, probably because there was no universal browser support for it. But we might have to revisit this to see if now it can be exposed.
At least for MS Edge and Firefox I have just successfully tested a tri-state TWebCheckBox...
As I said, we will revisit it to see if it is sufficiently universal