A name needs to be qualified when it is not exported by its defining module, or if more than one imported module has exported it.
Qualifying the name of a global variable by the module name can also serve to make the variable accessible inside a procedure or function where the name has been redefined. However, the recommended style is to start global variable names with capital letters and local variable names with small letters.
If a module has not been imported, its name cannot be used to qualify another name. However, a module need not import itself.
See also some examples.