--- a/ttml2/spec/acknowledgements-current.txt	Sat Jan 17 21:02:53 2015 -0700
+++ b/ttml2/spec/acknowledgements-current.txt	Sun Jan 18 10:05:14 2015 -0700
@@ -1,10 +1,10 @@
-Glenn Adams,
 Thomas Bause-Mason,
 John Birch,
 Kees Blom,
 Bert Bos,
 Brad Botkin,
 Dick Bulterman,
+Cyril Concolato,
 Frans de Jong,
 Mike Dolan,
 Martin Dürst,

--- a/ttml2/spec/ttml2-changes.html	Sat Jan 17 21:02:53 2015 -0700
+++ b/ttml2/spec/ttml2-changes.html	Sun Jan 18 10:05:14 2015 -0700
@@ -344,6 +344,9 @@
   inheritable and non-inheritable properties, use of specified initial
   value overrides, and root style inheritance.
 
+* In 10.13.14, make units component of a <length> expression optional,
+  which, if absent, is interpreted as if 'px' were specified.
+
 * In 11.1.2, require out-of-line region to specify 'xml:id' attribute.
 
 * In 11.3.1, qualify default region in terms of out-of-line region(s).
@@ -352,6 +355,9 @@
 
 * In 12.2.2, specify that a duration (@dur) of zero is explicitly permitted.
 
+* In 12.3.1, make metric component of a <timeExpression> expression optional,
+  which, if absent, is interpreted as if 's' were specified.
+
 * In 13.1.1, add 'animation' element in order to support out-of-line animation
   specifications.
 

--- a/ttml2/spec/ttml2.xml	Sat Jan 17 21:02:53 2015 -0700
+++ b/ttml2/spec/ttml2.xml	Sun Jan 18 10:05:14 2015 -0700
@@ -12523,7 +12523,7 @@
   | <loc href="#style-value-percentage">&lt;percentage&gt;</loc>
 
 scalar
-  : <loc href="#style-value-percentage">&lt;number&gt;</loc> units
+  : <loc href="#style-value-percentage">&lt;number&gt;</loc> units?
 
 units
   : "px"
@@ -12536,8 +12536,8 @@
 </tr>
 </tbody>
 </table>
-<p>It is an error to omit the units component of a scalar length
-value.</p>
+<p>If no <emph>unit</emph> is specified in a &lt;length&gt; expression, then it is to be treated as
+if a unit of <code>px</code> (pixels) were specified.</p>
 <p>The semantics of
 the unit of measure <code>px</code> (pixel) 
 are as defined by <bibref ref="xsl11"/>, &sect; 5.9.13.</p>