string substring(string, number, number?) : The substring function returns the substring of the first argument starting at the position specified in the second argument with length specified in the third argument. For example, substring("12345",2,3) returns "234". If the third argument is not specified, it returns the substring starting at the position specified in the second argument and continuing to the end of the string. For example, substring("12345",2) returns "2345". More precisely, each character in the string (see [3.6 Strings]) is considered to have a numeric position: the position of the first character is 1, the position of the second character is 2 and so on. The returned substring contains those characters for which the position of the character is greater than or equal to the second argument and, if the third argument is specified, less than the sum of the second and third arguments; the comparisons and addition used for the above follow the standard IEEE 754 rules.