The meaning of this input?
 

Hi, I am applying surface tension to melting of a 3d wall. The top face, which is irradiated by a heat source, has the following option in the boundary conditions:

https://i.imgur.com/HWu1koQ.jpg

The "surface tension gradient" option, is used to denote a surface tension coefficient in the fluid.
Now, while studying surface tension in 3D, we have to study it along both of the axis, (x and z in this case)
Does this apply the surface tension coefficient in both x and z directions? If no, then how do I do it?