my @sects= qw( 1 2 2.2 2.13 2.1.7 3.4a 10.1
    10.10 10.1a 1a.2 );
my $maxdigs= 4;
my %sects;
foreach my $sect (  @sects  ) {
    ( my $sort= $sect ) =~ s/(\d+)/
        sprintf "%0$maxdigs.$maxdigs"."d", $1 /ge;
    $sects{$sort}= $sect;
}
print join( " ", @sects{ sort keys %sects } ), "\n";