envelope flaps (features)

An extension of the cover of a book which folds across the fore-edge of the bookblock and over the opposite side of the cover (except on Islamic bindings where the envelope flap was traditionally placed under the opposite cover). The leading edge of such flaps was often given a triangular profile, thus resembling the traditional shape of the flap of an envelope. Fore-edge envelope flaps may extend from either the left or right side of the cover and may or may not be secured with a fastening. Envelope flaps (features) are extensions of the covering material, i.e. part of a single piece of cover material. Envelope flaps formed by separate pieces are defined in the Language of Bindings thesaurus as envelope flaps (components).