I have built and installed floor cabinets with a nicely finished
quartersawn oak top. Now I am ready to install bookcases on top of
them. The cases will be anchored to the wall but I'd also like to
secure the vertical sides of the bookcase to the oak cabinet top. The
cases are painted plywood (to match existing built-ins) so, if
necessary, holes can be filled and painted over. Pocket screws
through the sides down into the top? Biscuits? Other? Thanks!

Kevin