[css-display] Define in-flow/out-of-flow.

Author: fantasai

css-display/Overview.bs

@@ -701,9 +701,10 @@ Appendix A: Glossary</h2>
 
 		<dt><dfn lt="atomic inline|atomic inline box">atomic inline</dfn>
 		<dd>
-			An inline-level box that is replaced or that establishes a new formatting context.
-			(An inline-level box whose <a>inner display type</a> is not ''flow''
-			establishes a new formatting context of the specified <a>inner display type</a>.)
+			An inline-level box that is replaced (such as an image)
+			or that establishes a new formatting context (such as an ''inline-block'' or ''inline-table'').
+			Any inline-level box whose <a>inner display type</a> is not ''flow''
+			establishes a new formatting context of the specified <a>inner display type</a>.
 
 		<dt><dfn lt="block container|block container box">block container</dfn>
 		<dd>
@@ -788,6 +789,16 @@ Appendix A: Glossary</h2>
 			Often used to refer to a <a>block formatting context</a> <em>root</em>,
 			that is, a <a>block box</a> that establishes a new <a>block formatting context</a>
 			for its contents.
+
+		<dt><dfn>out-of-flow</dfn>
+		<dt><dfn>in-flow</dfn>
+		<dd>
+			A box is <a>in-flow</a> if it is floated (via 'float')
+			or absolutely-positioned (via ''absolute'' or ''fixed'' positioning).
+			A box is <a>in-flow</a> if it not <a>out-of-flow</a>.
+
+			Note: some formatting contexts inhibit floating,
+			so that an element with ''float: left'' is not necessarily <a>out-of-flow</a>.
 	</dl>
 
 	See [[!CSS2]] <a href="http://www.w3.org/TR/CSS2/visuren.html">Chapter 9</a> for a fuller definition of these terms.