makefiles: obj vs. objtree

[Randy Dunlap <rdunlap@xenotime.net>]

Can someone clarify the difference(s) in these variables, please?

Documentation/kbuild.txt says about objtree:

$(objtree) is the directory where output files are saved.
The output directory is often set using "O=..." on the commandline.


Documentation/makefiles.txt says about obj:

    $(obj)
	$(obj) is a relative path which points to the directory
	where the target is saved. Always use $(obj) when
	referring to generated files.


These appear to be the same to me, but let me be more specific:

In some cases (or places), Documentation/DocBook/Makefile uses
$(obj) and other cases/places, it uses $(objtree).
Does it have these correct, or should some of them be fixed?

thanks,
-- 
~Randy