[css-content-3] Define 'match-parent' for 'quotes' w3c#5478

Author: fantasai

css-content-3/Overview.bs

@@ -390,12 +390,12 @@ Specifying quotes with the 'quotes' property</h4>
 
 	<pre class='propdef'>
 		Name: quotes
-		Value: auto | none | [ <<string>> <<string>> ]+
+		Value: auto | none | match-parent | [ <<string>> <<string>> ]+
 		Initial: auto
 		Applies To: all elements
 		Inherited: yes
 		Percentages: n/a
-		Computed Value: the keyword ''quotes/none'', the keyword ''quotes/auto'', or a list, each item a pair of string values
+		Computed Value: the keyword ''quotes/none'', the keyword ''quotes/auto'' or ''quotes/match-parent'', or a list, each item a pair of string values
 		Animation type: discrete
 	</pre>
 
@@ -428,6 +428,18 @@ Specifying quotes with the 'quotes' property</h4>
 			however it is encouraged to submit any improvements to Unicode
 			so that the entire software ecosystem can benefit.
 
+		<dt><dfn>match-parent</dfn>
+		<dd>
+			Specifies the same [=quotation mark system=] as the the parent.
+			In general this is equivalent to inheriting the parent's [=computed value=],
+			except that ''quotes/auto'' it resolves
+			using the same [=content language=] that the parent used.
+
+			Issue: Two possible approaches here, currently speccing the latter:
+			a) this computes to the relevant string values, and inherits as such.
+			b) this value effectively inherits as a keyword + a language code,
+			meaning ''quotes/auto'', but with this language.
+
 		<dt>[ <<string>> <<string>> ]+
 		<dd>
 			The [=quotation mark system=] is defined as
@@ -1335,6 +1347,8 @@ bookmark-state</h3>
 		<li>Updated ''quotes/auto'' to reference the <em>parent</em> [=content language=]
 			rather than the [=content language=] of the element itself.
 			(<a href="https://github.com/w3c/csswg-drafts/issues/5478">Issue 5478</a>)
+		<li>Added ''quotes/match-parent'' value to 'quotes'.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/5478">Issue 5478</a>)
 		<li>Miscellaneous editorial spec clean up.
 	</ul>