DTD questions

Hi,

I'm creating modular DTDs and in this mind would like to be able to use 
Parameter Entities.

What I want to do is simple :

<!ENTITY % test "(oneElem|theOther)">
<!ELEMENT root %test;>

I try with xerces, microsoft and xmlspy  parser that all refuse this.



Of course, in ths example, I'm able to have a workaround :

<!ENTITY % test "oneElem|theOther">
<!ELEMENT root (%test;)>


But my real application is something like :
<![%isInclud;[
	<!ENTITY % test "(oneElem|theOther)">
]]>
<!ENTITY % test "EMPTY">
<!ELEMENT root %test;>

That's the reason why I need to have the parenthesis within the entity.

Any idea on this problem ? Any idea on how to solve it ?

Thanks,

Pierre