Number of first observation.
Number of last observation.
Comma separated list of observation numbers. Colons indicate a range. For example, `1,2,4:6,10' means 1,2,4,5,6,10.
File name of a flat ASCII text file containing a list of observation files to be reduced, one file per line. Path information should be either relative to $ORAC_DATA_IN, or the absolute path.
ORAC-DR: Overview and General Introduction