[selectors-4][editorial] Removed trget-within() from list of "new since Selectors 3" because it was removed

Author: svgeesus

selectors-4/Overview.bs

@@ -5322,7 +5322,7 @@ Changes Since Level 3</h3>
 		<li>Added '':is()'' and '':where()'' and '':has()''.
 		<li>Added '':scope''.
 		<li>Added '':any-link''.
-		<li>Added '':target-within'', '':focus-within'', and '':focus-visible''.
+		<li>Added '':focus-within'', and '':focus-visible''.
 		<li>Added '':dir()''.
 		<li>Expanded '':lang()'' to accept wildcard matching and lists of language codes.
 		<li>Expanded <css>:nth-child()</css> to accept a selector list.

selectors-4/Selectors _4_Explainer.md

@@ -0,0 +1,91 @@
+# Selectors 4 Explainer
+
+## Authors
+
+ - Chris Lilley (W3C)
+
+## Participate
+- [Issue tracker](https://github.com/w3c/csswg-drafts/issues?q=state%3Aopen%20label%3A%22selectors-4%22)
+
+## What are Selectors
+
+Introduced with [CSS1](https://www.w3.org/TR/CSS1/#basic-concepts) in 1996,
+Selectors are a mature and widely deployed way to
+select **individual parts** of a (typically HTML) document,
+so that they may be **styled** or **manipulated with script**.
+
+They were further developed in [CSS2.1](https://www.w3.org/TR/CSS2/selector.html#q5.0) 
+(W3C Recommendation, from 2011)
+and in [Selectors 3](https://www.w3.org/TR/selectors-3/)
+(W3C Recommendation, 2018).
+
+[Selectors 4](https://www.w3.org/TR/selectors-4/)
+is now widely deployed, stable,
+and is being prepared for W3C Recommendation,
+while less-mature Selectors have been moved to
+[Selectors 5](https://www.w3.org/TR/selectors-5/).
+
+However, the Selectors 4 specification
+is a _complete specification_ of Selectors,
+(including material from levels 1 through 3)
+not a delta. This aids readability.
+
+In view of this widespread use,
+this explainer does not address early-review questions
+such as general user need or alternatives considered;
+instead it motivates the particular changes found in Selectors 4.
+
+## Why `Selectors` not `CSS Selectors`?
+
+Selectors have expanded beyond their initial use in CSS;
+they are also widely used in the Document Object Model,
+to select parts of a document for manipulation by JavaScript.
+These are both majority uses, hence the naming of the specification.
+
+## What is new in Selectors 4
+
+(Expanded from [Changes Since Level 3](https://drafts.csswg.org/selectors-4/#changes-level-3))
+
+### Conditional Logic
+
+- The matches-any [`:is`](https://www.w3.org/TR/selectors-4/#matches) pseudo-class,
+    formerly called `:matches()`,
+    has been added to allow stylesheet authors to group functionally related elements,
+    such as any element that is either hovered or focussed.
+
+### Interactivity and Forms
+
+### Hyperlinking Support
+
+- Added [`:any-link`](https://www.w3.org/TR/selectors-4/#the-any-link-pseudo) to match
+    any element that acts as the source anchor of a hyperlink
+
+### Clearer Expression of Authorial Intent
+
+- Expanded the sibling-counting [`:nth-child()`](https://www.w3.org/TR/selectors-4/#the-nth-child-pseudo) 
+    and negation [`:not()`](https://www.w3.org/TR/selectors-4/#negation) pseudo-classes
+    to accept a **selector list**.
+
+### Internationalization Improvements
+
+- Expanded the content language [`:lang()`](https://www.w3.org/TR/selectors-4/#the-lang-pseudo) pseudo-class
+    to accept **wildcard matching** and **lists of language codes**.
+- 
+
+### Consolidation
+
+Selectors first introduced in
+[CSS Basic UI 3](https://www.w3.org/TR/css-ui-3/),
+such as 
+have been moved to the main Selectors 4 specification.
+
+## Further reading
+
+For further information on the use of Selectors in CSS 
+(covering all levels, but with a focus on level 4), see 
+[CSS Selectors](https://css-tricks.com/css-selectors/) on CSS-Tricks.
+
+For selectors in the DOM, see
+[NodeList](https://developer.mozilla.org/en-US/docs/Web/API/NodeList) on MDN.
+
+The [Horizontal Review of Selectors 4](https://github.com/w3c/csswg-drafts/issues/13469).