Explain focus-visible intent and guidance.

selectors-4/Overview.bs

@@ -2256,6 +2256,42 @@ The Focus-Indicated Pseudo-class: '':focus-visible''</h3>
 		like clicking on the button with a mouse pointer.
 	</div>
 
+	The goal of this selector is to explain how the browser's default focus
+	indicator behavior works in order to encourage more visible, usable focus
+	styles, and discourage the practice of disabling the default user agent focus
+	style.
+
+	For example, a `:focus` style will always be applied
+	to a focused element, regardless of _how_ it was focused. Whereas a
+	`:focus-visible` style would only be applied to an element if it matches the
+	same heuristic that the UA uses to draw its default focus indicator.
+
+	The user agent should take into account the available signals as to whether
+	the user might find focus indication useful. The result of these heuristics
+	must determine whether `:focus-visible` should match on the currently focused
+	element.
+
+	By default, if there are no signals indicating that focus should be
+	indicated, then focus should not be indicated on the focused element, unless
+	the user has expressed a preference for always seeing a focus ring.
+
+	The following may be considered signals:
+
+	* An element which requires the use of a keyboard, such as a text input,
+	should always have a visible focus indicator.
+	* If a user is using keyboard-based navigation by using the tab and arrow
+	keys, the focused element should be indicated. 
+	* If a user is interacting with an element via the keyboard (such as
+	incrementing or decrementing using the arrow keys, or using the spacebar to
+	activate a button) the focused element should be indicated.
+		* Note that keyboard interaction may trigger focus to be moved
+		programmatically, and this may be considered an extension of the original
+		keyboard interaction.
+
+	Because `:focus-visible` must match the UA's default behavior for when to show
+	a focus indicator, one way to meet this requirement would be to use
+	`:focus-visible` in the UA stylesheet itself.
+
 	<div class=advisement>
 		Page authors should follow these guidelines
 		when deciding whether to use '':focus'' or '':focus-visible''
@@ -2271,30 +2307,6 @@ The Focus-Indicated Pseudo-class: '':focus-visible''</h3>
 			use '':focus-visible''.
 	</div>
 
-	When UAs choose to specially indicate focus on an element,
-	or whether they specially indicate focus at all,
-	is UA-dependent.
-	Different UAs,
-	the same UA on different operating systems,
-	or the same UA on the same OS,
-	but with different user settings,
-	can make different choices as to when an element matches '':focus-visible''.
-
-	<div class=example>
-		The following guidelines are suggested heuristics
-		for choosing when to apply '':focus-visible''
-		to elements without “native” focus indicator behavior:
-
-		* If the element received focus via a keyboard interaction,
-			including indirectly,
-			such as triggering a dialog
-			by pressing a button using the keyboard,
-			apply '':focus-visible''.
-		* If a keyboard event occurs while an element is focused,
-			even if the element wasn't focused by a keyboard interaction,
-			apply '':focus-visible''.
-	</div>
-
 <h3 id="the-focus-within-pseudo">
 The Focus Container Pseudo-class: '':focus-within''</h3>