incorporate author 'should' for naming draggable elements

[scottaohara]

in html an element can be given the draggable attribute, and presently the HTML spec says the following:

An element with a draggable attribute should also have a title attribute that names the element for the purpose of non-visual interactions.

this isn't explicitly covered in the element naming steps right now, and maybe that's fine. But wanted to create this issue so that potential instances of where the combination of title + draggable might need to be called out could be double checked.