A Checkbox is a field that toggles between two states, open and closed. The oopen(on) and closed(off) state of the field has a direct correlation to the
on and off states of the AP (appearance stream) of the Annotation.
class CheckBox extends Field {
new(page: Page, fieldIndex: number): CheckBox
new(form: Form, annotation: Annotation): CheckBox
checked: boolean
}Construct a CheckBox from an existing object. The CheckBox Annotation must already exist in the Page's
Annotations Dictionary. This constructor will create the instance given the index of the Annotation
in the Page's Annotations Dictionary. If the index value is less than zero or greater than the length
of the Page's Annotations Dictionary (see annotationsCount) a Range Error will be thrown.
new(page: Page, fieldIndex: number): CheckBoxCreate a new CheckBox from an Annotation and owned by the Form. The Annotation must be
a Widget type annotation.
new(form: Form, annotation: Annotation): CheckBoxToggle the AS property of the checkbox annotations dictionary; AS values maybe one of ON or OFF.