{
{   The purpose of this request is to open a file for display output.  The file
{ is opened for append access (and shorten access if possible).  The file's
{ file_contents attribute must "list" or "legible" or "unknwon".  If it is
{ "list" each displayed line will have a "format effector" automatically
{ prefixed to it.
{
{   This request initializes a DISPLAY_CONTROL variable that holds state
{ information concerning the display.  The fields of this variable should never
{ be modified directly, always call the appropriate display request.  Certain
{ fields may, however, be usefully interrogated.  These are PAGE_WIDTH,
{ PAGE_LENGTH, PAGE_FORMAT and DEVICE_CLASS.  The display requests themselves
{ ignore PAGE_WIDTH and DEVICE_CLASS but PAGE_WIDTH should be used by most
{ display producers in order to tailor their output to the dimensions of the
{ output device or file.  The PAGE_LENGTH and PAGE_FORMAT fields are used to
{ automatically control the pagination of the display.  Unless you need to
{ place "page footers" in the output (see deck clh$vertical_tab_display) you
{ can ignore the PAGE_LENGTH field.  Unless you are imbedding "header" or
{ title-like information in the body of the display, you can ignore the
{ PAGE_FORMAT field.
{
{       CLP$OPEN_DISPLAY_REFERENCE (FILE, NEW_PAGE_PROCEDURE,
{         DEFAULT_FILE_CONTENTS, DEFAULT_RING_ATTRIBUTES, DISPLAY_CONTROL,
{         STATUS)
{
{ FILE: (input)  This parameter specifies the file to used for display output.
{
{ NEW_PAGE_PROCEDURE: (input)  This parameter specifies the procedure to be
{       called each time a new page of the display is about to be started.
{       This procedure may place "footer" information at the bottom of the
{       current page (if PAGE_NUMBER is greater than zero).  The procedure is
{       responsible for calling clp$reset_for_next_display_page.  It may then
{       put title information at the top of the new page (e.g.  using
{       clp$build_standard_title).  Alternativlely, the standard
{       clp$new_page_procedure may be specified.  See its header deck for more
{       information.  If NIL is specified only clp$reset_for_new_display_page
{       is called to start a new page.
{
{             NEW_PAGE_PROCEDURE (DISPLAY_CONTROL, NEW_PAGE_NUMBER, STATUS)
{
{       DISPLAY_CONTROL: (input, output)  This parameter specifies the
{             display_control variable initialized when the display was opened.
{
{       NEW_PAGE_NUMBER: (input)  This parameter specifies the number for the
{             page that the NEW_PAGE_PROCEDURE is to start.
{
{       STATUS: (output)  This parameter specifies the request status.
{
{ DEFAULT_FILE_CONTENTS: (input)  This parameter specifies the file_contents
{       attribute value to be used if this open request creates the file.
{       Usually this is specified as FSC$LIST.
{
{ DEFAULT_RING_ATTRIBUTES: (input)  This parameter specifies the ring
{       attributes to be used if this open request creates the file.  Normally,
{       the three ring attributes are set to the current ring of execution.
{       This parameter provides the means for a privileged process to created a
{       display file for a less privileged process.
{
{ DISPLAY_CONTROL: (output)  This parameter specifies the variable which
{       maintains state information for the display.
{
{ STATUS: (output)  This parameter specifies the request status.
{
