Impose Dirichlet pressure booundary conditions in kspaceFirstOrder3D

I actually saw in the reference,

"Modelling Nonlinear Ultrasound Propagation in Absorbing Media using the k-Wave Toolbox: Experimental Validation"

it describes in short as follows:

"Input pressure signals were assigned to source.p
and enforced as a time-varying Dirichlet boundary condition
over a 10 × 15 mm plane within the computational grid by
setting source.p_mode = ‘dirichlet’. "

A naive approach is to assign the temporal signal by setting

source.p = pressure signals;
source.p_mode = 'dirichlet';

Is there any relevant examples to explain how to do this?

Thanks

k-Wave

A MATLAB toolbox for the time-domain
simulation of acoustic wave fields