Contains all (exported and non-exported) objects, and is a descendent of
R_GlobalEnv. The hierarchy is <namespace:pkg>,
<imports:pkg>, <namespace:base>, and then
R_GlobalEnv.
ns_env(pkg = ".")package description, can be path or package name. See
as.package for more information
If the package is not loaded, this function returns NULL.
pkg_env for the attached environment that
contains the exported objects.
imports_env for the environment that contains
imported objects for the package.