tell and seek may be used to jump around in the single __DATA__ section.

Quite true. I'm just going to throw in the mention that tell() really is needed if you are planning to seek() your way through *DATA. Simply because *DATA is an extension of your file, so seek DATA, 0, 0; brings you to the start of the file, rather than the start of the __DATA__ section. (P.S.: I gather that you already knew this, as per your mention of tell(). Just wanted to throw in the extra info for anyone who stumbles across this and wonders how to do such a thing).

#!c:/perl/bin/perl -w
$|++;

use strict;

# incorrect - maybe not what you expect
print scalar <DATA>;
seek DATA, 0, 0;     # seeks to first line of file!
print scalar <DATA>;

__DATA__
foo
bar
[download]

#!c:/perl/bin/perl -w
$|++;

use strict;

# correct
my $start = tell DATA; # tells us where __DATA__ begins

print scalar <DATA>;
seek DATA, $start, 0;  # seek to the saved point
print scalar <DATA>;

__DATA__
foo
bar
[download]