data-type specifies the data type of the strings; the following values are allowed: text specifies that the sort keys should
be sorted lexicographically in the culturally correct manner for the language specified by lang number specifies that the
sort keys should be converted to numbers and then sorted according to the numeric value; the sort key is converted to a number
as if by a call to the number function; the lang attribute is ignored, a QName with a prefix is expanded into an expanded-name
as described in [2.4 Qualified Names]; the expanded-name identifies the data-type; the behavior in this case is not specified
by this document. The default value is text.
Examples (xslt:xml): Overview 18:4