For more details regarding the concepts discussed in this section and developing applications based the Xt intrinsics, see [7,9]. For a description of the C language interface to the Xt intrinsics, see [1]. For a description of the C language interface to the Athena widget set, see the ``Athena Widget Set --- C Language Interface'' documentation, distributed by the X Consortuim. For applications developed using the Motif widget set, see [7,2,4]. For a description of the C language interface to the Motif widget set, see [3].