--- a/ttml10/spec/ttaf1-dfxp.xml	Wed Jun 19 15:30:27 2013 +0800
+++ b/ttml10/spec/ttaf1-dfxp.xml	Wed Jun 19 16:38:40 2013 +0800
@@ -4668,9 +4668,6 @@
 </tr>
 </tbody>
 </table>
-<p>An <loc href="#style-value-alpha">&lt;alpha&gt;</loc> value greater
-than 1.0 must be considered equivalent to an <loc
-href="#style-value-alpha">&lt;alpha&gt;</loc> value of 1.0.</p>
 <p>The <att>tts:opacity</att> style is illustrated by the following example.</p>
 <table id="style-attribute-opacity-example-1" role="example">
 <caption>Example Fragment &ndash; Opacity</caption>
@@ -6064,6 +6061,8 @@
 then it must be interpreted as equal to 0.0; similarly, if the value
 represented is greater than 1.0, then it must be interpreted as
 1.0. The value NaN must be interpreted as 0.0.</p>
+<p>A specified value for &lt;alpha&gt; should not be <code>NaN</code>,
+less than 0, or greater than 1.</p>
 <p>If a presentation processor does not support a specific,
 valid opacity value, then it must interpret it as being equal to the
 closest supported value.</p>

--- a/ttml10/spec/ttml-changes.html	Wed Jun 19 15:30:27 2013 +0800
+++ b/ttml10/spec/ttml-changes.html	Wed Jun 19 16:38:40 2013 +0800
@@ -136,6 +136,8 @@
 * In 8.2.9, add note with example of using percentage on font size on root element.
 * In 8.2.9, clarify that a negative value in a font size is not valid.
 * In 8.2.12, clarify that a negative value in a line height is not valid.
+* In 8.2.13, remove redundant requirement to threshold alpha value greater than 1.0
+  since this is already mandated in 8.3.1.
 * In 8.2.14, remove "if specified, or the external authoring context, if not specified"
   from the first paragraph, since there is always a defined root container region.
 * In 8.2.16, clarify that a negative value in a padding is not valid.
@@ -145,6 +147,9 @@
 * In 8.3, add paragraph indicating that linear whitespace (LWSP) is not implied or
   permitted between tokens of style value expressions defined thereunder unless
   explicitly specified.
+* In 8.3.1, specify that alpha value should not be NaN, less than 0, or greater than
+  1. N.B. the use of "should" not "must". Such out of range values are not invalid,
+  and are thresholded to the supported range, but should nevertheless not be used.
 * In 8.3.4, remove contents of section since no normative (or other) use is made
   of a <duration> syntax expression. Leave empty section in place in order
   to prevent renumbering sections.