[css-variables-1] Animation-tainted props are infectious. w3c#1737

Author: tabatkins

css-variables-1/Overview.bs

@@ -174,6 +174,10 @@ Defining Custom Properties: the '--*' family of properties</h2>
 	becomes <dfn>animation-tainted</dfn>,
 	which affects how it is treated when referred to via the ''var()'' function in an animation property.
 
+	[=Animation-tainted=] is "infectious":
+	custom properties which reference [=animation-tainted=] properties
+	also become [=animation-tainted=].
+
 	<div class='example'>
 		This style rule: