Count of unique elements [XSLT 1.0]

Hi all,

The XML:

	<product>
		<prodid>V667320</prodid>
		<name>Battery Pack</name>
		<price>$20</price>
		<quantity>178</quantity>
		<region>SouthWest</region>
	</product>
	<product>
		<prodid>M382932</prodid>
		<name>CD Visor Organizer</name>
		<price>$19</price>
		<quantity>129</quantity>
		<region>NorthWest</region>
	</product>
	<product>
		<prodid>U3923839</prodid>
		<name>Rock n Roll Supercart</name>
		<price>$150</price>
		<quantity>200</quantity>
		<region>SouthWest</region>
	</product>
	<product>
		<prodid>Q3929302</prodid>
		<name>Digital Tire Guage</name>
		<price>$40</price>
		<quantity>623</quantity>
		<region>NorthWest</region>
	</product>

I want to count the unique elements 'region' into XML. In this example
the count result must be "2" - there's two unique 'region': NorthWest
and SouthWest.

Any help is appreciated.

BR
Plamen