Question: Changing the coordinate system in the Physics package for Maple

I am trying to write a metric in Maple 2019, using the Physics package in Cartesian coordinates. I know that there is already a pre-installed way in which to set the coordinates to Cartesian, namely, if we have something like 

Setup(coordinates=cartesian);

or similarly, using the Coordiantes calling sequence, such that we may define something like

Coordinates(A=cartesian);Setup(coordinates=A);

yet, if I am not mistaken, this gives the coordinates in the following form: {x,y,z,t}, yet I seek to define the metric in the following, perhaps more arbitrary coordinate system, {x1,x2,x3,t}. Is there any way to setup the coordinate system to read like the set I just described, such that I can then take a norm of these three spatial coordaintes to be |x|? Any help would be greatly appreciated.