use feature qw( say );
   use Sort::Key::Natural qw( natsort );
   say for natsort qw( 	P007b_Yum P007_Yum  );
   say qw(---);
   say for natsort qw( 	P007B_YUM P007_YUM  );
   say qw(---);
   say for natsort qw( 	P007b_yum P007_yum  );
   

##</code><code>##

P007_Yum
P007b_Yum
---
P007B_YUM
P007_YUM
---
P007b_yum
P007_yum