Thank you all, I did some test to confirm all your points. Here are the scripts to document this:

use strict;
use foo;

print "From <DATA>:\n";
print <DATA>;

print "From <foo::DATA>:\n";
print  <foo::DATA>;

print "From <bar::DATA>:\n";
print <bar::DATA>;


__DATA__
a
b
c
[download]

Here's the foo.pm:

package foo;
use strict;

package bar;

1;
__DATA__
1
2
3
4
[download]

Running the first script gives:

From <DATA>:
a
b
c
From <foo::DATA>:
From <bar::DATA>:
1
2
3
4
[download]