A plurality of convex strip portions are formed on a front surface of a light guiding plate, extending in a direction from a light incidence plane to an opposite side surface. For example, the height of the ground contact lead portions may be increased to further isolate signal contacts in adjacent columns from interfering electrical fields. Upon detection of the placement of an insertion pointer within a paragraph of text in the document, an editing surface is created overlaying the paragraph in the window and containing the contents of the underlying paragraph.