[css-sizing] Fix one usage to 'behaves as auto', and add a catch-all note to redirect appropriately.

Author: tabatkins

css-sizing-3/Overview.bs

@@ -312,9 +312,14 @@ New Keywords for 'width' and 'height'</h3>
 	'width'/'height' computes to ''width/auto''
 	and when it is defined to behave as ''width/auto''
 	(as in the case above),
-	the property is said to <dfn export lt="behave as auto|behaving as auto">behave as auto</dfn>
+	the property is said to <dfn export lt="behave as auto|behaves as auto|behaving as auto">behave as auto</dfn>
 	in both of these cases.
 
+	Note: Legacy spec prose defining layout behavior
+	might explicitly refer to 'width'/'height' having a computed value of ''width/auto'' as a condition;
+	these should be interpreted as meaning <a>behaves as auto</a>,
+	and reported to the CSSWG for updating.
+
 <h3 id='the-contain-floats-value'>
 Containing Floats</h3>
 
@@ -470,7 +475,7 @@ Stretch-fit Sizing</h3>
 
 	Percentages specify sizing of a box with respect to the box’s <a>containing block</a>.
 	When calculating the <a>intrinsic size contribution</a> of the box,
-	intrinsic sizes are instead treated as ''width/auto''.
+	intrinsic sizes instead behave as ''width/auto''.
 
 	<div class="example">
 		For example, in the following markup:
@@ -484,7 +489,7 @@ Stretch-fit Sizing</h3>
 		</pre>
 
 		When calculating the width of the outer div,
-		the inner div is treated as ''width: auto'',
+		the inner div behaves as ''width: auto'',
 		so the outer div sets itself to the width of the long word.
 		Since the outer div's width didn't depend on "real" layout,
 		though, it's treated as <a>definite</a>
@@ -493,9 +498,10 @@ Stretch-fit Sizing</h3>
 	</div>
 
 	Although this may require an additional layout pass to re-resolve percentages in some cases,
-	the ''min-width/auto'', ''min-width/min-content'', ''min-width/max-content'', and ''min-width/fit-content'' values
-	of 'min-width' and 'min-height'
-	do not prevent the resolution of percentage sizes of the box’s contents.
+	a 'min-width' or 'min-height'
+	with a value of ''min-width/min-content'', ''min-width/max-content'', ''min-width/fit-content'',
+	or ''min-width/auto'' (or otherwise <a>behaving as auto</a>)
+	does not prevent the resolution of percentage sizes of the box’s contents.
 	However, in order to prevent cyclic sizing in the general case,
 	percentages do not otherwise resolve against <a>indefinite</a> sizes,
 	and instead are treated as <css>auto</css>.