public FunctionSignature(QName name, SequenceType[] arguments, SequenceType returnType) { this(name, null, arguments, returnType);
public FunctionSignature(QName name) { this(name, null, DEFAULT_TYPE, false);
	public FunctionSignature(QName name, SequenceType[] arguments, SequenceType returnType) {		this(name, null, arguments, returnType);	}