Check box form fields belong to the generic class of form field called "Toggle Buttons". They are most commonly used for supporting On/Off or True/False type data values, although they are not restricted to these value types. Multiple check boxes can be in the same state simultaneously, independent of their parent objects. A specific check box type (the 3-state type), supports the three-valued logic states, "On", "Off" and "Null" (i.e. neither "On" nor "Off").
Check boxes can be text-based or image-based. Text check boxes are displayed as the familiar "check box" immediately followed by some descriptive text. The value state of a text check box is "On" if an "X" is present in the box portion, "Off" if no "X" is present in the box portion, and "Null" if the box portion is gray-filled. Image check boxes are displayed as an image with no associated text or box portion. The value state of an image check box (more appropriately, "image toggle button") is determined by which one of the two (or three, if a 3-state), possible images is displayed. The physical dimensions of an image check box are controlled by the selected automatic sizing option.