>> Are there absolute pointing devices with a z axis?

Yes.  Most mice, for example, though admittedly the Z axis support is
minimal - typically only two positions are sensed.

:-)  But seriously, there are such things.

> I am aware of the existance of 3d mice, but I don't know what X does
> with such things.

The core protocol has no support for more than two axes in the pointing
device; it's full of structures with two fields for coordinates.  Look
at almost any pointer event, for example, or the QueryPointer reply.

ISTR seeing an Input extension which could support such a thing as
three valuators....

					der Mouse

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