Any byte, anywhere in the file.

One thing to note is that seek resets the state of the filehandle, including errors, eof, as well as Perl's internal idea of whether or not it should append the filehandle to any warnings or error messages (see Re: Closing and re-opening the DATA Filehandle). That's why you might see the no-op seek (seek $fh, 0, 1) used occasionally for such things.

bbfu
Seasons don't fear The Reaper.
Nor do the wind, the sun, and the rain.
We can be like they are.