Indicates that a widget which is ENABLED and SENSITIVE has a value which can be read, but not modified, by the user.
Note that this state should only be applied to widget types whose value is normally directly user modifiable, such as check boxes, radio
buttons, spin buttons, text input fields, and combo boxes, as a means to convey that the expected interaction with that widget is not
possible. When the expected interaction with a widget does not include modification by the user, as is the case with labels and
containers, ATK_STATE_READ_ONLY should not be applied. See also ATK_STATE_EDITABLE. Since: ATK-2-16