Older packages may not conform to this rule (no subdirectories) and
for these there may be a hierarchy of subdirectories within the
package directory itself. In these cases all ``externally visible''
include files will be found in one of the following standard places:
Numerous problems with compilers and debuggers have meant that these
freedoms are no longer recommended and all new packages should put
everything in a single package (version) directory.
- a subdirectory with the same name as the package, or
- a subdirectory named