--- a/master/masking.html	Tue Jul 31 15:59:28 2012 +0900
+++ b/master/masking.html	Tue Jul 31 15:59:28 2012 +0900
@@ -703,6 +703,13 @@
 
 <h4 id="MaskValues">Calculating mask values</h4>
 
+<p class="note">
+The ability to use the alpha of a mask source as the mask values is new
+in SVG 2.
+In SVG 1.1 masks always use the luminance of the mask source as the mask
+values.
+</p>
+
 <p>
 A mask source may be interpreted using one of two different methods with regards
 to calculating the mask values that will be multiplied with the target alpha