       1mcindex 4m22mstring24m 4mindexExpr0m
              Returns  the character indexed by the expression 4mindexExpr24m (zero
              based) from 4mstring24m.

              If the expression 4mindexExpr24m starts with the string 1mend22m, then 1mend0m
              is  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.
