use Sort::Key::Maker iikeysort => qw(integer integer);
@sorted = iikeysort { /^(\d+)x(\d+)$/ } @a;

##</code><code>##

use Sort::Key::Multi 'iikeysort';
@sorted = iikeysort { /^(\d+)x(\d+)$/ } @a;

##</code><code>##

use Sort::Key::Multi 'isikeysort';
@sorted = isikeysort { /^(\d+)(\w+)(\d+)$/ } @a;