QBE search for blanks

What is the syntax to search for a blank field for a grid column?

I've so far found using <-1 seems to work okay...

Curious.

appending to that question - what's the hack to QBE by a list of items?

Somewhere - I saw a client QBE a form by a list of choices - basically placing the list within the qbe and getting them back. I cannot remember the syntax they used (or if it was a hack)... it would be nice for a refresher - if someone knows.

TIA

(db)