--- a/user-interface-safety.html	Fri Oct 18 23:51:13 2013 +0000
+++ b/user-interface-safety.html	Fri Oct 25 18:56:03 2013 +0000
@@ -24,7 +24,7 @@
         // subtitle   :  "an excellent document",
 
         // if you wish the publication date to be other than today, set this
-        // publishDate:  "2009-08-06",
+        publishDate:  "2013-10-25",
 
         // if the specification's copyright date is a range of years, specify
         // the start date here:
@@ -716,9 +716,19 @@
    
     <p>If the number of the pixels which are different 
     between the screenshots don't exceed a
-    the percentual threshold defined by the
+    percentage threshold defined by the
     <code>tolerance</code> property of the <code>input-protection</code> directive,
-    return. Otherwise, assume that the DOM element which the user is
+    return. </p>
+
+    <p>Differences are computed at a pixel-by-pixel level. Any difference in the value
+    of a pixel and it does not match.  For example, a protected area in blue
+    overlayed entirely by cross-origin content in red at 1% opacity is considered to
+    be 100% different, not 1% different. 
+    If portions of the <strong><em>control image</em></strong> are clipped by 
+    the view port or otherwise occluded, all such pixels must be
+    considered not to match.</p>
+
+    <p>Otherwise, if the differences exceed the tolerance, assume that the DOM element which the user is
     interacting with has been obstructed or obscured by a UI Redressing
     attempt and proceed with step 4.</p>
 
@@ -821,13 +831,17 @@
 set of common pixels for the fully rendered page.  The <strong><em>control
 image</em></strong> can be acquired through operating system APIs or from the
 compositor for the outermost document context.
-These images are compared, and if the differences are below the
+These images are compared, and if the number of pixels that differ are below the
 <code>tolerance</code> threshold associated with the <code>input-protection</code>
 directive, proceed to deliver the event normally, otherwise proceed to
-<strong>Violation management</strong>.  If portions of the <strong><em>control
-image</em></strong> are clipped by the root view port in the outermost
-document's coordinate system or otherwise occluded, all such pixels must be
-considered not to match.
+<strong>Violation management</strong>.  
+
+    <p>Differences are computed at a pixel-by-pixel level. Any difference in the value
+    of a pixel and it does not match.  For example, a protected area in blue
+    overlayed entirely by cross-origin content in red at 1% opacity is considered to
+    be 100% different, not 1% different.  If portions of the <strong><em>control
+    image</em></strong> are clipped by the view port or otherwise occluded, all such pixels must be
+    considered not to match.</p>
 </li>
 
  <li><strong>Violation management</strong> -