Trying to add new keyword to design table?

Hi,

I am trying to add a new keyword to my design table called "Stud" but when I enter it into my design table, SolidWorks states that I am using an invalid keyword. I decided to use the available "comment" keyword instead...

Can I create custom keywords for my design table? 

How do I do that? Is it a custom properties thing?

Any input appreciated. 

See pictures for more info.

SolidworksGeneral