The first (or only) post type object selected in the UI.
An object to allow sient failure, if the post type has not been selected.
Implements MPFT::forward to return the first post type, regardless of whether or not the field is setup to allow multiple post types to be selected (iterator-related methods are setup to regard the multiple items though). This allows calls to be made on the field object directly as if the field is a post type object itself.
Note: This method is intended for internal use and should not be called directly.