add a note on min/max line length and nested flexboxes

Author: alexmog1

css3-flexbox/Overview.src.html

@@ -1563,6 +1563,15 @@ <h3 id='main-sizing'>
 					the size of a flexbox item is its hypothetical outer main size, 
 					clamped according to its min and max main size properties.
 					Repeat until all flexbox items have been collected into flexbox lines.
+					<p class="note">
+					Note
+					that parent layout must be able to suppress clamping to 
+					specified min/max-width/height. For example, if parent 
+					layout is also a flexbox and flexbox layout is being 
+					calculated at the step requiring unconstrained &#39;auto&#39; height 
+					of items, min/max-width/height properties on flexbox must 
+					not be consulted at this step.
+					</p>
 			</ul>
 
 		<li>