If the source_strg does not contain sub_strg, the function returns the empty string. Otherwise, it finds the first occurence of sub_strg and returns the pert of source_strg that follows the occurence. If any argument is not a string, it is converted to string using rules for string() XPATH function.
String
Extract time and timezone ("23:59:59 GMT" substring) from timestamp
substring-after('1999-12-31 23:59:59 GMT',' ')