REPLACESTRING - replace part of string.

ReplaceString (S1,I1,S2[,I2]) returns S

deletes part of string S1 and inserts string S2 in place of the deleted characters. I1 gives the position of the first character to be deleted; the character at the beginning of S1 has an index of 0. I2 gives the number of characters to be deleted. If I2 is -1, ReplaceString deletes from position I1 to the end of string S1. If I2 is omitted, ReplaceString determines the length of S2 and deletes that many characters.