[css-cascade-5][editorial] Replace source order with order of appearance

Author: mirisuzanne

css-cascade-5/Overview.bs

@@ -1210,7 +1210,7 @@ Cascade Layers</h3>
 	overrides, and other styling concerns--
 	and are able to re-order the cascade of layers in an explicit way,
 	without altering selectors or specificity within each layer,
-	or relying on source-order to resolve conflicts across layers.
+	or relying on order of appearance to resolve conflicts across layers.
 
 	<div class="example">
 		For example, the following generates an explicit ''reset'' layer,
@@ -1233,7 +1233,7 @@ Cascade Layers</h3>
 		The unlayered declarations on the <{audio}> element take precedence
 		over the explicitly layered declarations on <code>audio[controls]</code> --
 		even though the unlayered styles have a lower specificity,
-		and come first in the source order.
+		and come first in the order of appearance.
 	</div>
 
 	Name-defining [=at-rules=]