The DDS Display File keyword, CLRL avoids clearing the display before writing the record format to that display. Normally any existing screen format is erased unless OVERLAY is used and the new format does not contain output on any line that the existing screen occupies.
CLRL goes beyond that by not clearing the existing screen at all. Thus allowing you to write stuff that overlays existing screen content.
The CLRL keyword accepts one parameter, which can be a variety of options, including:
When using CLRL( ) you may also need to include the RSTDSP(*YES) keyword on the CRTDSPF CL command when creating the display file. I say "may" because its often necessary depending on the program flow in your shop and the other display formats on the screen.