yea so its interesting, i tried it with just " " at first, at didn't work because when you render the data node, the generic xform xmlns gets put in there, despite it not being in the source xml.

(relatedly: i most likely don't need the `replacing` parameter, and could just always replace the `xform.data_node.tag_xmlns` (since that returns the generic_xmlns when theres no xmlns in the xml), but i felt this might be more explicit)