[MapProxy] XYZ support (TMS w/ y-axis inverted)

[Billy Newman]

Does map proxy support XZY servers, i.e.:

This Open Street Map server serves out tiles in XYZ format
http://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png

I would like to merge tiles from the above server with tiles from another XYZ server.  Is it possible w/ MapProxy to merge 2 XYZ servers (layers) and server out one layer that include both?

Thanks,
Billy