@Override
    public String toString() {
        return "(" + start + ' ' + end + ')';
    }
Returns the character n places (0 base) before the start of the value substring into the superstring.
For example charBefore(0) returns the first character before the start of the substring

@return the char n planes before the start of the substring
@throws IndexOutOfBoundsException if the string does not have a character at this position
container-search/src/main/java/com/yahoo/prelude/query/Substring.java