Any of these variables that are defined by common.make can and should be used by the user’s makefile fragments to reference directories and/or perform any tasks which are not done automatically by the Makefile Package. Most variables refer to directory paths, both absolute and relative, where files will be installed, but other variables are defined based upon the target platform that the person is compiling for. Do not change the values of any of these automatically defined variables as the resultant behaviour of the Makefile Package is undefined.