|Synopsis:||The name of an #include guard shall contain at least the name of the header file.|
If projects have files with the same name in different directories, it is not possible to include both files. The guard of an internal header file must have an additional underscore appended at the end. This is to prevent duplicate guard names when a certain interface is specified by both an internal and external header file that have the same name. See also [ORG#001].