diff --git a/css-ui/Overview.bs b/css-ui/Overview.bs
--- a/css-ui/Overview.bs
+++ b/css-ui/Overview.bs
@@ -1458,7 +1458,22 @@ Finally if the UA does not support any o
 and simply render the ''pointer'' cursor.
 </div>
 
+<h5 id="cursor_of_root">Cursor of the root element</h5>
 
+The document <a href="http://www.w3.org/TR/CSS21/intro.html#the-canvas">canvas</a>
+is the infinite surface over which the document is rendered [[!CSS21]].
+Since no element corresponds to the canvas,
+in order to allow styling of the cursor when not over any element,
+the cursor of the root element becomes the cursor of the canvas.
+However, if no boxes are generated for the element
+whose cursor would be used for the canvas
+(for example, if the root element has ''display: none''),
+then the canvas cursor is the platform-dependent default cursor.
+
+Note: An element might be invisible,
+but still generate boxes. For example,
+if the element has ''visibility: hidden'' but not ''display: none'',
+boxes are generated for it and its cursor is used for the canvas.
 
 <h3 id="keyboard">Keyboard control</h3>