-# This method is supposed to be called inside the source root directory.
-# Use $this->get_buildpath($path) method to get full path to the files
-# in the build directory.
+# Generally, it is enough to look for invariant unique build system
+# files shipped with clean source to determine if the source might
+# be buildable or not. However, if the build system is derived from
+# another other auto-buildable build system, this method
+# may also check if the source has already been built with this build
+# system partitially by looking for temporary files or other common
+# results the build system produces during the build process. The
+# latter checks must be unique to the current build system and must
+# be very unlikely to be true for either its parent or other build
+# systems. If it is determined that the source has already built
+# partitially with this build system, the value returned must be
+# greater than the one of the SUPER call.