Marks major changes in the output format of the files produced by the
compiler. Files produced be different major versions are considered
incompatible and will not be used as source of class information.
Indicates a change in the compiler that does not affect the output
format. Source files will be prefered over class files build by
compilers with different minor versions, but if no source file is
available, then the class file will be used.
Denote minor changes and bugfixes to the compiler. Class files compiled
with versions of the compiler that only differ in patchlevel (from the
current instantiation) will always be preferred over source files
(unless the source files have newer modification dates).