SFL processing

[P.Goovaerts@xxxxxxxxxx]

I have a basic DSPF/SFL-processing question which I hope will be answered
here.  (It's not Code400 specific)

this is how it works now:
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I have a SFL with 50 records.
Screen display's topline (1st page).
I enter option '3' on the 3rd record
then I scroll to the 4th page
I enter option '2' in the 2nd record
finally I press enter inputoptions are checked/processed
user get's an error the option on first page is not valid

When the user uses pageup/pagedown, he is scrolling through the subfile
without entering the program.

but

I want an errormessage when user enters '3' followed by pageup/pagedown
without processing

QUESTION:
Is it possible to check the options when the user users pageup/pagedown
- without 'processing' the program logic
- without using specific function keys (i.e. 'F7/F8')
- without using the 'Values' keyword in DDS like this:
               ZSEL           1A  B  7  2VALUES(' ' '1' '2' '4' '7')

a good example of what I want is the behaviour of the 'Work With Members'
-panel.
When a user enters '10' and presses 'PageDown', he get's a message that
this is not a valid option, however when entering a correct option, it is
not processed immediatly.