[selectors-4] Add :autofill w3c#5775

Author: fantasai

selectors-4/Overview.bs

@@ -2553,6 +2553,13 @@ The Placeholder-shown Pseudo-class: '':placeholder-shown''</h4>
 		whenever such placeholder text is shown.
 	</div>
 
+<h4 id="autofill">
+The Automatic Input Pseudo-class: '':autofill''</h4>
+
+	The <dfn>:autofill</dfn> pseudo-class represents input elements
+	that have been automatically filled by the user agent,
+	and have not been subsequently altered by the user.
+
 <h4 id="the-default-pseudo">
 The Default-option Pseudo-class: '':default''</h4>
 
@@ -4013,6 +4020,8 @@ Changes since the 21 November 2018 Working Draft</h3>
 			(<a href="https://github.com/w3c/csswg-drafts/issues/3821">Issue 3821</a>)
 		<li>Added '':muted'' and '':volume-locked'' sound state pseudo-classes.
 			(<a href="https://github.com/w3c/csswg-drafts/issues/3821">Issue 3821</a> and <a href="https://github.com/w3c/csswg-drafts/issues/3933">Issue 3933</a>)
+		<li>Added '':autofill''.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/5775">Issue 5775</a>)
 		<li>Added '':user-valid''.
 			(<a href="https://lists.w3.org/Archives/Public/www-style/2015Sep/0111.html">Discussion</a>)
 		<li>Defined '':is()'', '':where()'', '':has()'', '':nth-child()'', and '':nth-last-child()''
@@ -4177,5 +4186,13 @@ Acknowledgements</h2>
 Privacy and Security Considerations {#priv-sec}
 ==============================================
 
-This specification introduces no new privacy or security considerations,
-as selectors do not provide any ability not already possible by walking the DOM manually.
+This specification introduces the following privacy and security considerations:
+<ul>
+	<li>
+		The '':visited'' pseudo-class can expose information about which sites a user has previously visited,
+		if the UA is not careful to screen from scripting any information that would reveal
+		which elements match it.
+	<li>
+		The '':autofill'' pseudo-class can expose whether a user has interacted with this form before;
+		however the same information can be derived by observing how quickly the form is filled out.
+</ul>