ult is based on
 the Java system locale. The only collating sequence supplied with the SAXON product is "en" (English),
 but other values may be supported by writing a user-defined comparison class. If no comparison class
 is found for the specified language, a default algorithm is used which simply sorts according
 to Unicode binary character codes. The value of lang does not have to be a recognized language
 code, it is also possible to use values such as "month" to select a data-type-specific collat