[selectors-4] Document changes since Selectors 3

Author: xfq

selectors-4/Overview.bs

@@ -3941,6 +3941,42 @@ Changes</h2>
 	Note: The 1 February 2018 draft included an inadvertent commit of unfinished work;
 	2 February 2018 has reverted this commit (and fixed some links because why not).
 
+	Significant changes since the <a href="https://www.w3.org/TR/2012/WD-selectors4-20120823/">23 August 2012 Working Draft</a> include:
+
+	<ul>
+		<li>Added '':blank'' and '':placeholder-shown'' pseudo-classes.
+		<li>Released some restrictions on '':matches()'' and '':not()''.
+		<li>Defined fast and complete Selectors profiles (now called <a>live</a> and <a>snapshot</a>).
+		<li>Improved definition of <a>specificity</a> to better handle <a>:matches()</a>.
+		<li>Updated grammar.
+		<li>Cleaned up definition of <<An+B>> notation.
+		<li>Added definition of <a>scope-relative</a> selectors, changed <i>scope-constrained</i> to scope-filtered for less confusion with scope-contained.
+		<li>The '':local-link()'' pseudo-class now ignores trailing slashes.
+	</ul>
+
+	Significant changes since the <a href="https://www.w3.org/TR/2011/WD-selectors4-20110929/">29 September 2011 Working Draft</a> include:
+
+	<ul>
+		<li>Added language variant handling per RFC 4647.
+		<li>Added scoped selectors.
+		<li>Added <css>:user-error</css> (now called '':user-invalid'').
+		<li>Added <css>:valid-drop-target</css>.
+		<li>Changed <a>column combinator</a> from double slash to double pipe.
+	</ul>
+
+	Additions since <a href="https://www.w3.org/TR/css-cascade-3/">Level 3</a>:
+
+	<ul>
+		<li>Added '':dir()''.
+		<li>Added <css>:nth-match</css>.
+		<li>Made '':indeterminate'' normative.
+		<li>Added column selectors.
+		<li>Added '':scope''.
+		<li>Added '':any-link''.
+		<li>Added case-insensitive attribute-value matching.
+	</ul>
+
+
 <h2 id="acknowledgements">
 Acknowledgements</h2>