The variable NEXTLINE contains the index of the current entry in the table EXTRACT. NEXTLINE is
the index of the entry to be processed in the loop in the overview screen.
the index of the entry displayed in the detail screen. The value is determined by the variable FIRSTLINE and L, where
FIRSTLINE is the index of the first line displayed on the overview screen
L is the line number on the overview screen on which the function F2 was called.