I don't actually know what the proper term is, but what I'm talking about is when you shrink the width to a certain point, and the page starts sliding back and forth because some setting is too wide.

Unless you are purposely building a site with horizontal scrolling, this is always a frustrating thing to come across. Usually I have to dig through every single item and check all of the width settings, and often each item's grid settings before I find the culprit.

It would be cool to have a warning that surrounds the item in red, or at least pops up a warning at the top with a link that takes you to the offending setting, similar to how it now tells you if you don't have the box for country in a checkout page.

You could also have a "I'm making a horizontally scrolling page" button that would turn it off for that page.