http://hlkitwiki.wolflair.com/index.php5?title=Creatures_(Savage_Worlds)
Here's a page from the Savage Worlds walkthrough that discusses this - the part you're looking for is a few paragraphs from the end, where it discusses Existence tag expressions.
Here's the general wiki page discussing them, although it doesn't have any examples, which is why i started with the walkthrough:
http://hlkitwiki.wolflair.com/index....Tag_Expression