-the targets src/directory/all and src/directory/clean build and clean
-only the specified directory, each directory has its own Makefile that
-invokes the top level make with src/directory/foo for the foo target,
-so it is possible to work only under a specific test directory
+the main non-file make targets are all, run, clean and cleanall.
+(cleanall removes the reports unlike clean, run reruns the dynamically
+linked executables)
+
+make variable can be overridden from config.mak or the make command line,
+the variable B sets the build directory which is src by default
+
+for each directory under src there are targets like $(B)/directory/all,
+$(B)/directory/run and $(B)/directory/clean to make only the contents
+of that directory, each directory has its own Makefile set up so it
+invokes the top level make with B=src src/directory/foo for the foo
+target, so it is possible to work only under a specific test directory