An element can be local to a module or global to a profile. The element is globally defined when it is referenced by more than one module, for example, defined in the top-level module. Each module “exports” all its local elements as externals in its header file.
This allows other user modules to access them. If you want to reference an element you must refer to its scope by including the appropriate header file. An example is shown below.
If you want to reference (for example) an element BAUD_RATE in module display, you should include the header file “display.h” to make the element visible.