Weak Constraints from COMSOL 3.5 to 4.2a

Hi

I have seen many posts regarding this but none had any definite answer.

I am trying to follow a tutorial which involving Stoke's flow, and have the following problems:

1. "Go to Properties of mmglf model and turn Weak constraints -> On and Constraint type -> Nonideal"

I have found out that the mmglf module is the same as spf module of 4.2a with the Stoke's flow check box checked. I have also found out that I can add a "Weak Constraint" node to the spf module. But I don't know if this should be the volume "Weak Contraint" node or the surface one. Also in the node, Contraint type can be set either to "Bidirectional" or "User-defined" (not Unidirectional which is non-ideal). How do I set it to "Nonideal"?

Note: "Nonideal Weak Constraint" is used to automatically calculate the hydrodynamic stress on the particle surface.

2. "Options Menu | Expressions | Boundary Expressions"

How do I write Boundary Expressions? I feel Coupling Variables is to be used, but I am not sure how. I was only able to find Integration/Summation to the boundaries.

Please help. Relevant images are attached.