Before sewing, the pages of a books must be pressed firmly, to expel air and also to crease the folds of the sheets. Books are to be trimmed before sewing. There are various styles of sewing. Stabbing is the most primitive of these. Oversewing (also called 'overcastting or whipstiching') was developed in the eighteenth century to hold heavy plate books together firmly. It is a method for making a series of sections, then sewing all along them. Oversewing machines are the mainstays of modern library binders.