Mesh <Hidden Shadows> property in path tracing

Hi,
do you know how to turn on the ‘hidden shadows’ mesh property for path tracing? I am not able to make this work, there is no word in the documentation on this, nor on google…

I was also thinking on a workaround, to make transparent material that would cast full shadow, unfortunately not that of a material wizard to pull that of.

I am grateful for any insight