You don't have to do it that way. You can embed arbitrary foreign (but appropriately namespaced) XML into an XHTML document and style it with CSS, untransformed

You don't have to do it that way. You can embed arbitrary foreign (but appropriately namespaced) XML into an XHTML document and style it with CSS, untransformed. Or, as the sibling comment says, you can even avoid XHTML and style pure XML directly.