public char charAfter(int n) {
        return string.charAt(end+n);
    }
Returns the character n places (0 base) after the end of the value substring into the superstring.
For example charAfter(0) returns the first character after the end of the substring

@return the char n planes after the end of the substring
@throws IndexOutOfBoundsException if the string is not long enough to have a character at this position
container-search/src/main/java/com/yahoo/prelude/query/Substring.java