Displays a heading.
Each Heading control will create a visual border wrapping all other fields underneath it. This group is terminated if a control of type Heading, Separator, Heading with checkbox, or Heading (Collapsible) is encountered.
Each control in a heading's control group will implicitly inherit the visibility of the heading control.
In this example, "Car info" is the heading, with three textboxes inside it.
The JavaScript value of this control will always be null.