String Identifiers (StringIDs) are a special type of output data used to represent some of the strings that the z/OS XML parser encounters during a parse. A StringID is a 4 byte numeric value used to represent a complete string of text, thereby substantially reducing the size of the parsed data stream for documents containing frequently recurring strings, like namespace references. StringIDs can only be used if the optional StringID exit service is activated. For more information on StringIDs, see String Identifiers.