Sort lines in region numerically by the ARGth field of each line.
Fields are separated by whitespace and numbered from 1 up.
Specified field must contain a number in each line of the region,
which may begin with "0x" or "0" for hexadecimal and octal values.
Otherwise, the number is interpreted according to sort-numeric-base.
With a negative arg, sorts by the ARGth field counted from the right.
Called from a program, there are three arguments:
FIELD, BEG and END. BEG and END specify region to sort.
(fn FIELD BEG END)