[selectors-4] Defined language range (#13748)

* [selectors-4] Defined language range as BCP 47 extended language range, #13646

* [selectors-4][editorial] fix markup, #13748

Author: svgeesus

selectors-4/Overview.bs

@@ -2604,6 +2604,8 @@ The Language Pseudo-class: '':lang()''</h3>
 	represents an element whose [=content language=]
 	is one of the languages listed in its argument.
 	Each <dfn>language range</dfn> in '':lang()''
+	is an <a href="https://www.rfc-editor.org/rfc/rfc4647.html#section-2.2">extended language range</a>,
+	as defined in BCP 47, and
 	must be a valid CSS <<ident>> or <<string>>.
 	(Thus language ranges containing asterisks, for example,
 		must be either correctly escaped or quoted as strings,
@@ -5107,6 +5109,8 @@ Changes since the 11 November 2022 Working Draft</h3>
 
 	Significant changes since the <a href="https://www.w3.org/TR/2022/WD-selectors-4-20221111/">11 November 2022 Working Draft</a>:
 
+	* Defined language range as BCP 47 extended language range
+		(<a href="https://github.com/w3c/csswg-drafts/issues/13646"Issue  13646></a>)
 	* Removed the at-risk status from '':read-write'' and '':has()''
 	* Added '':popover-open'' pseudo-class.
 		(<a href="https://github.com/w3c/csswg-drafts/issues/8637">Issue 8637</a>)