{
{   The purpose of this request is to add a form to the list of forms
{ scheduled for display on the screen.  The next request that updates the
{ screen, fdp$xread_forms or fdp$xshow_forms, replots the screen.  The
{ added form lies on top of other forms scheduled for display occupying the
{ same area on the screen.  A pushed form cannot be added.
{
{       FDP$XADD_FORM (FORM_IDENTIFIER, STATUS)
{
{ FORM_IDENTIFIER: (input)  This parameter specifies the form to add to the
{       list of forms scheduled for display.
{
{ STATUS: (output)  This parameter specifies the name of the variable to set
{       to indicate the results of the request.
{
{       condition identifiers:  fde$bad_data_value
{                               fde$form_already_added
{                               fde$form_pushed
{                               fde$form_too_large_for_screen
{                               fde$invalid_form_identifier
{                               fde$no_space_available
{                               fde$system_error
{
