[css-cascade-3] Add note about applies-to on pseudo-elements; dfn applies-to #1861"

Author: fantasai

css-cascade-3/Overview.bs

@@ -442,14 +442,26 @@ Used Values</h3>
 		As another example, a <code>&lt;div></code> might have a computed 'break-before' value of ''auto'',
 		but acquire a used 'break-before' value of ''break-before/page'' by propagation from its first child. [[css-break-3]]
 
-	If the property does not apply to this element or box type
+	If the property does not <dfn lt="apply to | applies to">apply to</dfn>
+	this element or box type
 	(as defined by its “Applies To” line),
 	then it has no <a>used value</a> for that property.
 
 	<p class='example'>
 		For example, the 'flex' property has no <a>used value</a>
 		on elements that aren't <a>flex items</a>.
 
+	Note: A property defined to apply to “all elements”
+	applies to all elements and [=display types=],
+	but not necessarily to all [=pseudo-element=] types,
+	since pseudo-elements often have their own specific rendering models
+	or other restrictions.
+	The ''::before'' and ''::after'' pseudo-elements, however,
+	are defined to generate boxes almost exactly like normal elements
+	and are therefore defined accept all properties that apply to “all elements”.
+	See [[CSS-PSEUDO-4]]
+	for more information about [=pseudo-elements=].
+
 <h3 id="actual">
 Actual Values</h3>
 

css-cascade-4/Overview.bs

@@ -556,14 +556,26 @@ Used Values</h3>
 		As another example, a <code>&lt;div></code> might have a computed 'break-before' value of ''auto'',
 		but acquire a used 'break-before' value of ''break-before/page'' by propagation from its first child. [[css-break-3]]
 
-	If the property does not apply to this element or box type
+	If the property does not <dfn lt="apply to | applies to">apply to</dfn>
+	this element or box type
 	(as defined by its “Applies To” line),
 	then it has no <a>used value</a> for that property.
 
 	<p class='example'>
 		For example, the 'flex' property has no <a>used value</a>
 		on elements that aren't <a>flex items</a>.
 
+	Note: A property defined to apply to “all elements”
+	applies to all elements and [=display types=],
+	but not necessarily to all [=pseudo-element=] types,
+	since pseudo-elements often have their own specific rendering models
+	or other restrictions.
+	The ''::before'' and ''::after'' pseudo-elements, however,
+	are defined to generate boxes almost exactly like normal elements
+	and are therefore defined accept all properties that apply to “all elements”.
+	See [[CSS-PSEUDO-4]]
+	for more information about [=pseudo-elements=].
+
 <h3 id="actual">
 Actual Values</h3>