+specified portable file or scratch file.
+
+By default, cases excluded with FILTER are written to the
+file. These can be excluded by specifying DELETE on the UNSELECTED
+subcommand. Specifying RETAIN makes the default explicit.
+
+Portable files express real numbers in base 30. Integers are always
+expressed to the maximum precision needed to make them exact.
+Non-integers are, by default, expressed to the machine's maximum
+natural precision (approximately 15 decimal digits on many machines).
+If many numbers require this many digits, the portable file may
+significantly increase in size. As an alternative, the DIGITS
+subcommand may be used to specify the number of decimal digits of
+precision to write. DIGITS applies only to non-integers.