[css-align] Clarify that stretch is not proportional.

Author: fantasai

css-align/Overview.bs

@@ -376,7 +376,8 @@ Distributed Alignment: the ''<content-distribution>/stretch'', ''space-between''
 		<dt><dfn>stretch</dfn>
 		<dd>
 			If the combined size of the <a>alignment subjects</a> is less than the size of the <a>alignment container</a>,
-			any ''width/auto''-sized <a>alignment subjects</a> have their size increased equally so that the combined size exactly fills the <a>alignment container</a>,
+			any ''width/auto''-sized <a>alignment subjects</a> have their size increased equally (not proportionally)
+			so that the combined size exactly fills the <a>alignment container</a>,
 			and then clamped by their 'max-width'/'max-height' constraints.
 
 			The <a>alignment subjects</a> are then aligned as per ''flex-start''.

css-align/Overview.html

@@ -846,7 +846,8 @@ <h3 class="heading settled" data-level="3.3" id="distribution-values"><span clas
 		</dt>
         <dd>
 			If the combined size of the <a data-link-type="dfn" href="#alignment-subject">alignment subjects</a> is less than the size of the <a data-link-type="dfn" href="#alignment-container">alignment container</a>,
-			any <span class="css" data-link-for="width">auto</span>-sized <a data-link-type="dfn" href="#alignment-subject">alignment subjects</a> have their size increased equally so that the combined size exactly fills the <a data-link-type="dfn" href="#alignment-container">alignment container</a>,
+			any <span class="css" data-link-for="width">auto</span>-sized <a data-link-type="dfn" href="#alignment-subject">alignment subjects</a> have their size increased equally (not proportionally)
+			so that the combined size exactly fills the <a data-link-type="dfn" href="#alignment-container">alignment container</a>,
 			and then clamped by their <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css2/visudet.html#propdef-max-width">max-width</a>/<a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css2/visudet.html#propdef-max-height">max-height</a> constraints.