Irtsgbr

I tried to print labels with UTF-8 input. I have read, that this requires xetex. So I wrote the following example to write 1€ in the four corners of a 102mm x 152mm label:

pdfpagewidth=102mm
pdfpageheight=152mm

hsize=pdfpagewidth
vsize=pdfpageheight

advancehoffset by -1in
advancevoffset by -1in

parindent=0pt
nopagenumbers

fontcmuss="CMU Sans Serif" at 12pt
cmuss

1€hfill 1€
vfill
1€hfill 1€

bye

But the vfill does not work.

The second row is not at the bottom of the page but in the middle.

What did I wrong?

Just insert eject before bye. :-)

The explanation for what you saw is simply that bye is defined this way in plain TeX (TeXbook p. 357):

outerdefbyeparvfillsuperejectend

This is where the undesired vfill comes from.

Side note

There is a special rule used when TeX encounters end. I'm giving it here for reference, because this was the first thing I suspected, but it is not involved here. This rule is given in the TeXbook p. 264:

When TeX sees an end command, it terminates the job only if the
main vertical list has been entirely output and if deadcycles=0.
Otherwise it inserts the equivalent of

line vfill penalty-’10000000000

into the main vertical list, and prepares to read the end token
again. This has the effect of invoking the output routine repeatedly
until everything has been shipped out. In particular, the last column
of two-column format will not be lost.

Invoking the dangerous filll of "the highest infinity" (see p.72 of the TeXbook)

pdfpagewidth=102mm
pdfpageheight=152mm

hsize=pdfpagewidth
vsize=pdfpageheight

advancehoffset by -1in
advancevoffset by -1in

parindent=0pt
nopagenumbers

%fontcmuss="CMU Sans Serif" at 12pt
%cmuss

1€hfill 1€
vskip 0pt plus 1filll

1€hfill 1€

bye