The short form uses a structure with the name screen implicitly instead of
an explicitly declared work area wa. This is either the obsolete built-in
or a structure declared in the current context called screen, which must have the data type SCREEN.
The long form with an explicitly declared work area should be used instead of the short form.
The short form of the statement LOOP AT SCREEN behaves like the statement LOOP in a loop across an internal table with a
header line, where the built-in structure is used as the header line.