Adds a new SelectionFormField.

<void> FormFieldCollection.addSelectionFormField(<Number> emptyWidth, [<RequestSelectionFormFieldCallback> callback], [<ErrorCallback> errorCallback])


Parameter Description
emptyWidth Specifies the horizontal extension, in twips, of the SelectionFormField, when there is no selected item. When this parameter is set to 0, a default value is used.
callback Optional. Receives the added SelectionFormField.
errorCallback Optional. Is called when the operation failed with an error.