Be more specific about the linear keyword

css-easing-2/Overview.bs

@@ -418,8 +418,27 @@ It returns an [=output progress value=].
 
 <h3 id=the-linear-easing-keyword oldids=linear-timing-function-section>The linear easing keyword: ''linear''</h3>
 
-The <dfn dfn-type=value for=easing-function>linear</dfn> keyword is a shorthand
-for <a lt="linear()" function>linear(0, 1)</a>.
+The <dfn dfn-type=value for=easing-function>linear</dfn> keyword
+produces a [=linear easing function=]
+with two [=linear easing function/points=]:
+
+1.   : [=linear easing point/input=]
+     :: 0
+     : [=linear easing point/output=]
+     :: 0
+
+1.   : [=linear easing point/input=]
+     :: 1
+     : [=linear easing point/output=]
+     :: 1
+
+Note: This results in an identity function,
+meaning that its [=output progress value=] is equal to the
+[=input progress value=] for all inputs.
+
+Note: Although this produces a [=linear easing function=],
+it serializes as `linear`,
+as per the rules in [Serialization](#serialization).
 
 <h3 id=cubic-bezier-easing-functions oldids=cubic-bezier-timing-functions>Cubic
 B&eacute;zier easing functions:
@@ -714,8 +733,8 @@ defined in [[CSSOM]] with the following additional requirements:
 
 *   The keyword values ''ease'', ''linear'', ''ease-in'', ''ease-out'',
     and ''ease-in-out'' are serialized as-is, that is, they are
-    <em>not</em> converted to the equivalent ''cubic-bezier()''
-    function before serializing.
+    <em>not</em> converted to the equivalent ''cubic-bezier()'' or
+    ''linear()'' function before serializing.
 
 *   Step easing functions, whether they are specified using the
     ''steps()'' function or either of the ''step-start'' or ''step-end''