Ususally you can skip this section which describes obsolete, but still in effect aspects of Rep modules.
Modules marked as already imported into the current module is called
require imports a module only when its
feature is absent.
A list of the features, i.e. module names marked as imported into the current module. Each is a symbol.
Returns true if the feature feature has been loaded into the current module.
Don’t use this function unless you’re sure. Usually you don’t need it.
This function adds feature (a symbol) to the list of loaded features. A call to this function is normally one of the top-level forms in a file.