Call this subprocedure before RXS_parse() to tell the parser what encoding to use while parsing the character data in elements and attributes. By default the parser will look at the first few characters of the file to attempt to determine what encoding should be used. By default, and more often than not, UTF-8 is used. That can cause problems if the data was actually obtained using CCSID 819 (i.e. encoding ISO88591). If you are having trouble parsing characters like Ü then your data is probably being returned as ISO88591 vs. UTF-8 (as many XML declarations incorrectly state).
Note: An excellent reference for code pages can be found here.