[css2] update

--HG--
extra : convert_revision : svn%3A73dc7c4b-06e6-40f3-b4f7-9ed1dbc14bfc/trunk%402652

Author: fantasai

css2/issues/issues-4

@@ -234,6 +234,13 @@ Proposal 5:
 
 Proposal 6:
 
+  Line boxes that contain no text, no preserved white space, no inline
+  elements with non-zero margins, padding, or borders, and no other
+  in-flow content (such as images, inline blocks or inline tables),
+  and don't end with a line feed must be treated as zero-height line
+  boxes. For the purposes of margin collapsing, this line box must be
+  ignored.
+
 Resolution:
 
 =WG= Discuss.