Move contentful CSS image to own def

painttiming.bs

@@ -107,13 +107,17 @@ A [=generated content pseudo-element=] is a <dfn>paintable pseudo-element</dfn>
 * The pseudo-element's [=used=] [=opacity=] is greater than zero.
 * The pseudo-element generates a non-empty [=box=].
 
+A CSS [=image=] |img| is a <dfn>contentful image</dfn> when all of the following apply:
+* |img| is [=url valued=]
+* |img| represents a [=fully decodable image=]
+
 An [=element=] |target| is <dfn export>contentful</dfn> when one or more of the following apply:
 * |target| has a [=text node=] child, with at least one character, excluding [=document white space characters=].
 * |target| is a [=replaced element=] representing a [=fully decodable image=].
-* |target| has a [=background-image=] which is a [=url valued=] [=fully decodable image=], and its [=used=] [=background-size=] has non-zero width and height values.
+* |target| has a [=background-image=] which is a [=contentful image=], and its [=used=] [=background-size=] has non-zero width and height values.
 * |target| is a [=canvas=] with its [=context mode=] set to any value other than <code>none</code>.
 * |target| is an [=svg element with rendered descendants=].
-* |target| is an [=originating element=] for a [=paintable pseudo-element=] that represents a [=fully decodable image=] [=or text with at least one character excluding [=document white space characters=].
+* |target| is an [=originating element=] for a [=paintable pseudo-element=] that represents a [=contentful image=] or text with at least one character excluding [=document white space characters=].
 
 To compute the <dfn>paintable bounding rect</dfn> of [=element=] |target|, run the following steps:
     1. Let |boundingRect| be the result of running the [=getBoundingClientRect=] on |target|.