DzLine3 object

OK this is driving me a bit nuts at the moment (and probably because I'm missing something very fundamental). I can't use any methods on a DzLine3 object, I just get the "undefined is not a function errors...
 

(function(){

	var oLine = new DzLine3();
	oLine.origin = new DzVec3( 0,0,0 );
	oLine.end = new DzVec3( 1,1,1 );
	
	var nLength = oLine.length();
	print(nLength);
	
})();

always results in the follwoing output
 

Executing Script...
Script Error: Line 7
TypeError: Result of expression 'oLine.length' [undefined] is not a function.
Stack Trace: ()@:7
Error executing script on line: 7
Script executed in 0 secs 2 msecs.

What am I missing?