Using the "spatial at" function to extract a value at a particular point

I need to write a COMSOL expression to extract a result value at particular spatial coordinates from one study, so that the result can be used as input to another study.

I am trying to implement coupling between physics domains where the coupling is only understood empirically. The empirical model predicts the boundary conditions of physics B based on evaluating a particular result component (in this case a strain component) of physics A at a particular set of coordinates.

It looks like I should be able to use the "spatial at" function, but the documentation is a bit sparse.

The only example I can find is from page 227 of the COMSOL 5.0 reference guide, and it is largely unexplained:
root.comp1.at1(0,y,dom)
the digit after the 'at' is the dimensionality of the domain being evaluated over. In my case I am looking at a point, so that should be zero, correct? I am operating in 3-space so it should be something like
... scope.at0(xcoord,ycoord,zcoord, expr)

I am at a loss for understanding exactly how you define the scope? What exactly is root? Is it an alias for the root of the ModelBuilder tree?