E.2 says:

  # The canvas is transparent if contained within another, and given a
  # UA-defined color if it is not. It is infinite in extent and
  # contains the root element. Initially, the viewport is anchored with
  # its top left corner at the canvas origin.
  #
  # The painting order for the descendants of an element generating a
  # stacking context (see the 'z-index' property) is:
  #
  # 1. If the element is a root element:
  #    1. background color of element over the entire canvas.
  #    2. background image of element, over the entire canvas, anchored
  #       at the origin that would be used if it was painted for the
  #       root element.

and E.3 (Notes) says:

  # The background of the root element is only painted once, over the
  # whole canvas.


This fails to account for the special situation for the HTML BODY element described in 14.2:

  # The background of the root element becomes the background of the
  # canvas and covers the entire canvas, anchored (for
  # 'background-position') at the same point as it would be if it was
  # painted only for the root element itself. The root element does not
  # paint this background again.
  #
  # For HTML documents, however, we recommend that authors specify the
  # background for the BODY element rather than the HTML element.
  # For documents whose root element is an HTML "HTML" element or
  # an XHTML "html" element that has computed values of 'transparent'
  # for 'background-color' and 'none' for 'background-image', user
  # agents must instead use the computed value of the background
  # properties from that element's first HTML "BODY" element or XHTML
  # "body" element child when painting backgrounds for the canvas, and
  # must not paint a background for that child element. Such
  # backgrounds must also be anchored at the same point as they would
  # be if they were painted only for the root element.


E.2 should acknowledge 14.2 somehow.