This is an environment like <package:pkg>. The package
environment contains the exported objects from a package. It is
attached, so it is an ancestor of R_GlobalEnv.
pkg_env(package)package name.
When a package is loaded the normal way, using library(),
this environment contains only the exported objects from the
namespace. However, when loaded with load_all(), this
environment will contain all the objects from the namespace, unless
load_all is used with export_all=FALSE.
If the package is not attached, this function returns NULL.
ns_env() for the namespace environment that
all the objects (exported and not exported).
imports_env() for the environment that contains
imported objects for the package.