[xsl] Selecting the first node set

["Fraser Goffin" <goffinf@xxxxxxxxxxx>]

Given the following simplified XML instance, can anyone suggest an 
expression that will return ONLY the 'Value' node containing <enum> children 
with values A, B and C. I can't rely on the name of the parent node of 
<Value> hence I have deliberately named these as UnknownNameX or any other 
intervening structure.

<Trade>
	<UnknownName1>
		<Value>
			<enum>A</enum>
			<enum>B</enum>
			<enum>C</enum>
		</Value>
	</UnknownName1>
	<UnknownName2>
		<Value>/Trade//Value[ancestor::Trade]</Value>
	</UnknownName2>
	<Treatment>
		<UnknownName3>
			<Value>
				<enum>D</enum>
				<enum>E</enum>
				<enum>F</enum>
			</Value>
		</UnknownName3>
	</Treatment>
</Trade>


/Trade//Value        - returns all 3 <Value> nodes
/Trade//Value[1]    - also returns all 3 <Value> nodes (why is that ?)
/Trade//Value[2]    - returns nothing (why is that ?)

Cheers

Fraser.