bool isChecked

If this node has Boolean state that can be controlled by the user, whether that state is on or off, corresponding to true and false, respectively.

Source 

bool get isChecked => (_flags & SemanticsFlags.isChecked.index) != 0;
void isChecked=(bool value)

Source 

set isChecked(bool value) => _setFlag(SemanticsFlags.isChecked, value);