fgl_dialog_getbufferlength()
Returns the number of rows to feed a paged DISPLAY ARRAY.
Syntax
fgl_dialog_getbufferlength()
  RETURNS INTEGER
Usage
The fgl_dialog_getbufferlength() function returns the number
 of rows to be provided by the program to fill a page of a DISPLAY
 ARRAY running in paged mode.
This function must be called in the context of the ON FILL BUFFER
 trigger. The returned value is undefined if the function is used outside this
 trigger.