Reported by Anton Prowse, L. David Baron

Does the root element establish a block formatting context?  (It was believed to do so in 2002.[http://lists.w3.org/Archives/Public/www-style/2002Nov/0145.html]) According to the current spec, it doesn't seem to if its specified value is 'inline' or 'run-in', for example (in which case its computed value of 'display' is 'block').  Indeed, 9.4.1 seems to explicitly exclude the possibility:

   # Floats, absolutely positioned elements, inline-blocks, table-cells,
   # table-captions, and elements with 'overflow' other than 'visible'
   # (except when that value has been propagated to the viewport)
   # establish new block formatting contexts.

However, it does seem like there ought to be an initial block
formatting context since the definition of "block-level box" is roughly "a box which participates in a block formatting context".  More starkly, the issue affects whether the root element's height is computed using the rules in section 10.6.3 or the rules in section 10.6.7.  This difference in height is detectable using bottom-positioned background images, as reported in https://bugzilla.mozilla.org/show_bug.cgi?id=590491 

Note that the root element possesses all the characteristic properties
of an element which establishes a BFC, including in relation to margin
collapsing.

Bug description:
http://lists.w3.org/Archives/Public/www-style/2010Aug/0107.html
http://lists.w3.org/Archives/Public/www-style/2010Aug/0539.html



Issue 209: http://wiki.csswg.org/spec/css2.1#issue-209

Summary
    Does the root element establish a new block formatting context?
URI
    http://lists.w3.org/Archives/Public/www-style/2010Aug/0107.html
    http://lists.w3.org/Archives/Public/www-style/2010Aug/0539.html
Proposal
    The root element participates in a block formatting context
    established by the initial containing block.
Status
    Open. =errata= Deferred to Errata