case-order has the value upper-first or lower-first; this applies when data-type="text", and specifies that upper-case letters
should sort before lower-case letters or vice-versa respectively. For example, if lang="en", then A a B b are sorted with
case-order="upper-first" and a A b B are sorted with case-order="lower-first". The default value is language dependent.
Examples (xslt:xml): Overview 17:3