@{"$pkg\::_ATTR"} = @_

##</code><code>##

package pkg;
$_ATTR = 'I am $_ATTR from ' . __PACKAGE__;
package main;
$pkg = 'I am $pkg from ' . __PACKAGE__;

print "1. $pkg::_ATTR\n";
print "2. $pkg\::_ATTR\n";
print "3. ${pkg}::_ATTR\n";