Boolean toggle to include/exclude top level directory.

When preparing a package CPack installs the item under the so-called top level directory. The purpose of is to include (set to 1 or ON or TRUE) the top level directory in the package or not (set to 0 or OFF or FALSE).

Each CPack generator has a built-in default value for this variable. E.g. Archive generators (ZIP, TGZ, ...) includes the top level whereas RPM or DEB don’t. The user may override the default value by setting this variable.

There is a similar variable CPACK_COMPONENT_INCLUDE_TOPLEVEL_DIRECTORY which may be used to override the behavior for the component packaging case which may have different default value for historical (now backward compatibility) reason.