       1mcsubstr 4m22mstring24m 4mfirstExpr24m 4mlengthExpr0m
              Returns  a range of characters from 4mstring24m starting at the char-
              acter indexed  by  the  expression  4mfirstExpr24m  (zero-based)  for
              4mlengthExpr24m characters.

              If the expression 4mfirstExpr24m or 1mlengthExpr 22mstarts with the string
              1mend22m, then 1mend 22mis replaced with the index of the  last  character
              in  the  string.  If the expression starts with 1mlen22m, then 1mlen 22mis
              replaced with the length of the string.

              This command is UTF-aware.
