JAXP Transformer contract

Hi, 

I have a problem with a detail of the javax.xml.transformer.Transformer
specs. In our application we cache Templates objects and pool Transformer
objects just to keep things fast. This worked fine immediately but I had
problems with parameters until I realized there is a clearParameters() 
method, which helps a lot. Now I only wonder why one cannot reset a 
parameter with a given name? I.e.
	Transformer transformer = new Transformer();
	transformer.setParameter("abc", "b");
	//
	// do a transformation here 
	//
	transformer.setParameter("abc", "c");
I get with
	transformer.getParameter("abc") 
a result of
	"b"
instead of the 
	"c" 
I expected. This happens with Saxon 6.2.2, 6.3 and with
Xalan 2.0.1, so it seems to be intended by API. I cannot
imagine that this is useful and would like to know what
design idea is underlying ?!

I am just curious,
Thanx,
Frank

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