Commend Line to create Mid Surface

Hi Friends,

I have a doubt while using a command option to create midline.

I saw few videos in youtube they used commend line to create midline. When i try the same thing i cant able to get it. I shows the command is error. Is there any procedure to get it. Please help me out.

<?xml version="1.0" encoding="UTF-8"?>

This is the pic that i got from the youtube videos. It shows by writing command you can create midline.

<?xml version="1.0" encoding="UTF-8"?>

When i try the same i got this invalid command line.

What the problem with this. Can any one help me to solve it.

Thank you all in Advance waiting for your valuable comments.