Is there a standard description for the kinds of non-wheeled carry-on luggage (backpacks, satchels, totes, duffels) that have a sleeve or pocket that allow them to be fitted over the handle of a wheeled luggage piece?

(I'm talking about what is described here as a "rear pocket" (http://www.ebags.com/product/victori...uctid=10359052) or here as a "add-a-bag" (http://www.ebags.com/product/tumi/vo...uctid=10343496)).

I'm trying to figure out my options/sizing/brands but I can't find any consistent phrase to search for (and there are hundreds of bags on ebags, Amazon, luggagepros, etc - don't have time to open each listing up individually!).

Is there some terminology I can't think of that is commonly used to describe this feature on luggage? Or is it just descriptive text defined brand-by-brand?