[css-easing-2][editorial] Even better description of 'before start' flag. Add a linear easing to the bezier comparison.

Author: tabatkins

css-easing-2/Overview.bs

@@ -168,6 +168,12 @@ Some types of easing functions
 also take an additional boolean <dfn export for="easing function">before flag</dfn>,
 which indicates the easing has not yet started,
 or is going in reverse and is past the finish.
+(Some easing functions can have multiple possible [=output progress values=]
+for a given [=input progress value=],
+and generally favor the last one specified;
+this flag instead causes those [=easing functions=]
+to favor the first specified value
+before the animation has started.)
 
 This specification defines several types of easing functions:
 
@@ -640,13 +646,14 @@ The keyword values listed above are illustrated below.
     <thead>
       <tr><th>Easing<th>Example
     <tbody>
+      <tr><td>''linear''<td><div class=easing-track style="--easing:linear"></div>
       <tr><td>''ease-in''<td><div class=easing-track style="--easing:ease-in"></div>
       <tr><td>''ease-out''<td><div class=easing-track style="--easing:ease-out"></div>
       <tr><td>''ease-in-out''<td><div class=easing-track style="--easing:ease-in-out"></div>
       <tr><td>''ease''<td><div class=easing-track style="--easing:ease"></div>
   </table>
   <figcaption>
-    The above easing functions in action, each applied to a 3s animation of the circles' 'left' property.
+    The above easing functions in action, each applied to a 3s animation of the circles' 'left' property. A ''linear'' easing is provided for contrast.
   </figcaption>
 </figure>