Method and apparatus to correct an error of read-out data from a data storage medium, particularly a bit shift error, is described. The perimeter of each shroud includes an array of tabs or protrusions keyed to one of a corresponding array of skirted portals in the cassette cover. The second portion is movable relative to the first portion from a first position toward a second position to move the first and second bone portions away from each other. or higher; and II) a xylene soluble fraction at room temperature lower than 4% by weight, and a value of the ratio of the polymer fraction collected at 25 C.