[texhax] question about \vfil

[Matej Košík]

Hello,

Could somebody please explain me why this:

	\vfil abc\vfil\bye

doesn't have the same effect as this:

	\vbox to \vsize {
	        \vfil
        	abc
	        \vfil
	}
	\bye

The former one is simpler and thus nicer. But there \vfil-s seem to be
ignored. I do not understand why because as far as my humble knowledge,
TeX starts to process the input in vertical mode. So the initial \vfil
shouldn't be ignored.

I would really appreciate some explanation or some link to a relevant
information. I do not understand the horizontal/vertical mode stuff very
well.

Thanks in advance.
-- 
Matej Košík