A check box or a set of radio buttons: buttons with an on and an off state, whose value names the appearance state that is on.
public abstract class PdfToggleButtonField : PdfButtonField
ISO 32000-2 §12.7.5.2.3, §12.7.5.2.4 and Table 230. Each widget's normal appearance has its on state, under any name, and
optionally Off. The field's value V names the on state that is selected, Off when none is. Widgets select
their appearance with AS, which "shall also be" that value; when they disagree, AS decides the appearance and
V remains the value, and a ButtonValueStateMismatch diagnostic is recorded.
With Opt (PDF 1.4), entry i is the export value of the i-th widget in Kids, and on states may
be named by that position (/0, /1), so widgets can share an export value and still be told apart.
kind:method, kind:property, kind:ctor. Press Esc to clear.DefaultValueGets the state the field reverts to on a reset-form action (DV, inheritable), or null.ExportValueGets the export value of the selected state: the Opt entry of the first selected widget when there is an Opt, else the state's name; null when the value is Off.OnStateNamesGets the names of the widgets' on states, each once, in Kids order.OptionsGets the export value of each widget in Kids order (Opt, inheritable, PDF 1.4); empty when absent.SelectedWidgetsGets the widgets whose on state is the field's value: none when it is Off; several for duplicated check boxes or radio buttons in unison (which with Opt also includes widgets with the same export value).ValueGets the selected on state (V, inheritable); Off when the value is absent or nothing is selected.GenerateAppearances()Generates a normal appearance for each widget: an on and an Off appearance stream, the on one showing the widget's caption (MK CA) in ZapfDingbats; each widget's appearance state is set to match the value.GetAppearanceState(PdfWidgetAnnotation)Returns the appearance state widget shows: its AS; without one, the field's value when the widget has it as its on state, else Off.GetOnState(PdfWidgetAnnotation)Returns the on state of widget: the state of its normal appearance other than Off.GetWidgetExportValue(PdfWidgetAnnotation)Returns the export value of widget: its Opt entry when there is an Opt, else its on state's name.Select(PdfWidgetAnnotation)Turns widget on: the field's value becomes its on state, as when the user clicks it.SetExportValue(String?)Turns on the first widget whose export value is exportValue, or turns every widget off with null.SetValue(CosName)Selects the on state value, or nothing with Off: sets the field's value (V) and the appearance state (AS) of every widget that has appearance states.