> My confusion was that I couldn't understand why I have to 
> specify the type here yet not for a string, eg:
> 
> translate('ab-c', '-', '/')
> 

As with most other languages, XPath supplies built-in syntax for values of
some data types (string, integer, decimal, double) but not for others
(anyURI, QName, float, duration, boolean).

Michael Kay
http://www.saxonica.com/