Currently it seems I can build a list from only one Category at a time.

I choose that Category off the submenu for Show / Categories, which puts the little blue button next to that Category’s value. But then when I select a different category, the little blue button moves next to the new Category’s value. 

What I really need is to be able to keep the original little blue button where it is while adding more!

ie select more than one Category value at a time when building a list. Is this currently doable?

If not, this would go high on my A list for New Features, and you can move this post there.