{
{   The purpose of this request is to write sufficient empty lines to the
{ display such that the next line of data written to the display will appear on
{ the specified line of the page.  If data has already been written at or
{ beyond the specified line, clp$new_display_page is called prior to performing
{ this operation.
{
{   The most common use for this request is to place "footers" at the bottom of
{ display pages.  This requires that the PAGE_LENGTH field of the
{ DISPLAY_CONTROL variable be temporarily decremented by the number of lines
{ for the footer.  In a new_page_procedure, the original value of the
{ PAGE_LENGTH field is restored, clp$vertical_tab_display is called to "get to"
{ the first line for the footer, the footer is written, and the PAGE_LENGTH
{ field of the DISPLAY_CONTROL is again decremented.  The new_page_procedure
{ then calls clp$reset_for_next_display_page, and writes "header" (title) lines
{ on the top of the next page.
{
{       CLP$VERTICAL_TAB_DISPLAY (DISPLAY_CONTROL, LINE_NUMBER, STATUS)
{
{ DISPLAY_CONTROL: (input, output)  This parameter specifies the
{       display_control variable initialized when the display was opened.
{
{ LINE_NUMBER: (input)  This parameter specifies the number of the line to
{       which to tab.
{
{ STATUS: (output)  This parameter specifies the request status.
{
