substring
substring(str: String, start: Number, end: Number) : String
Returns the substring of string str starting from index start (inclusive) and ending at index end (exclusive).
For example,substring("abcdef", 0, 6) is "abcdef", substring("abcdef", 1, 3) is "bc",
and substring("abcdef", 1, 1) is "" (the empty string).