How does the model treat lateral boundary conditions when nothing is specified?

[MHBalsmeier]

I have a question I could not find an answer to anywhere:

What does WW3 assume on the boundary of a regional domain when nothing is specified?

From the handbook I could not find a real answer. In the documentation of w3_grid.inp I found

"If the actual input data is not defined in the actual wave model run, the initial conditions will be applied as constant boundary conditions",

but the way I understand it this only applies if boundary points are specified.
But when you specify

0 0 F

in the boundary section of ww3_grid.inp, what happens in this case?

I suspect that every spatial propagation scheme handles this differently. The spatial propagation scheme I use is UQ, so maybe Eqs. 3.21 and 3.22 are the answer in this case.

Could anyone help here?