ASBackgroundLayout overview has errors.

[jeffdav]

At: http://asyncdisplaykit.org/docs/layout2-layoutspec-types.html#asbackgroundlayoutspec

• "ASBackgroundLayoutSpec lays out a component (red), stretching another component behind it as a backdrop (blue)." It should be "component (blue)" and "backdrop (red)".
• "In the diagram below, the child is the blue layer." It's above, not below.
• "When using Automatic Subnode Management with the ASOverlayLayoutSpec, the nodes may sometimes appear in the wrong order." This looks like a copy/paste bug. Should be ASBackgroundLayoutSpec, not ASOverlayLayoutSpec. Assuming this is actually applicable here.