[css-ui-4] Make user-select optionally applicable to ::before and ::after

Author: frivoal

css-ui-4/Overview.bs

@@ -25,6 +25,7 @@ Abstract: This specification describes user interface related
           from the properties and values of previous CSS levels.
           It uses various properties and values
           to style basic user interface elements in a document.
+At risk: Applicability of 'user-select' to ''::before'' and ''::after''
 </pre>
 
 <h2 id="intro">Introduction</h2>
@@ -590,16 +591,35 @@ Omitted values are set to their initial values.
 		Value: auto | text | none | contain | all
 		Initial: auto
 		Inherited: no
-		Applies to: all elements
+		Applies to: all elements, and optionally to the ''::before'' and ''::after'' pseudo elements
 		Media: interactive
 		Computed value: See below
 	</pre>
 
 	User Agents must not apply the 'user-select' property to
 	the ''::first-line'' and ''::first-letter'' pseudo elements.
 
-	Issue: Whether 'user-select' should apply to ''::before'' and
-	''::after'' is an open question.
+	Note: The UA may apply this property to the ''::before'' and ''::after'' pseudo elements.
+	If it does, ''user-select/auto'' value computes to ''user-select/none'' on these pseudos,
+	but other values can be specified.
+	This preserves the legacy behavior of generated content not being selectable or copyable,
+	which is appropriate when these pseudos are used for decorative purposes.
+	However, this property allows them to become selectable and copyable,
+	as the user would expect in cases where they are used to generate part of the content,
+	such as the issue numbers in this document.
+	<strong class="advisement">To the extent possible,
+	authors should avoid using generated content
+	for non decorative purposes,
+	and should prefer including all the content in the DOM.</strong>
+	<em>This feature is at risk.</em>
+
+	When generated content in pseudo elements becomes selectable
+	through this mechanism,
+	UAs should also make this content findable through their search function.
+
+	Issue: Should it also apply to ''::marker''? To <a>page-margin boxes</a>?
+	Should the computed value of '''user-select/auto'' also be ''user-select/none'',
+	or would ''user-select/text'' be more appropriate?
 
 	The computed value is the specified value,
 	except:
@@ -628,6 +648,8 @@ Omitted values are set to their initial values.
 		<dt><dfn>auto</dfn>
 		<dd>The computed value of ''user-select/auto'' is determined as follows:
 		<ul>
+			<li>On the ''::before'' and ''::after'' pseudo elements,
+			the computed value is ''user-select/none''
 			<li>If the element is an <a>editable element</a>,
 			the computed value is ''contain''
 			<li>Otherwise,