string :str-sub ( string $STR , int $START , int $LENGTH )
string :str-sub ( string $STR , int $START )

Returns a portion of the original string, starting at character START and counting at most LENGTH characters.
If LENGTH is omitted, returns everything from the START-th character to the end of the string.

# :str-sub example
:set &NAME s''
:writeln s"What's your name?"
:readln &NAME
!if :eq s'v' :str-sub $NAME i2 i1
    :writeln s"The second letter of your name is 'v'!"
    :writeln s"Ain't that interesting?"
!else
    :writeln s'Good evening, ' $NAME s'.'
!fi