[web-animations-1] Re-introduce animation type definition

Author: birtles

web-animations-1/Overview.bs

@@ -2956,7 +2956,8 @@ property.
 
 Unless otherwise specified, all CSS properties are
 <dfn id="concept-animatable">animatable</dfn>.
-How property values combine is defined by the Animation line
+How property values combine is defined by
+the <dfn export>Animation type</dfn> line
 in each property's property definition table:
 
 <dl export>
@@ -3358,8 +3359,8 @@ referenced by a <a>keyframe effect</a> as one of its
             on <var>keyframe</var> with the result of combining
             <var>underlying value</var> (<var>V</var><sub>a</sub>) and
             <var>value to combine</var> (<var>V</var><sub>b</sub>)
-            using the <var>composite operation to use</var>
-            procedure defined by the <var>target property</var>'s
+            using the procedure for the <var>composite operation to use</var>
+            corresponding to the <var>target property</var>'s
             <a>animation type</a>.
 
     1.  If this <a>keyframe effect</a> has an <a>iteration