Draggable API clarification

[MagnusOxlund]

I've been going through the 4.0 docs, and I have some questions after reading the Draggable documentation chapter.

1. The x and y axis parameters accept objects consisting of other axis parameters. Apart from that, is there any practical difference between axis parameters and settings, or is the former just a semantic grouping of axis-related settings?
2. The options object parameter type that x and y accept aren't specified in the docs, but the code examples show the remaining 3 axis parameters used: snap, modifier, and mapTo. Are those the only valid options?

[MagnusOxlund]

See #1019