Merge pull request #1109 from w3c/issue-1108-units-scaling

Remove error condition from scaling procedures (#1108).

spec/ttml2.xml

@@ -15275,7 +15275,7 @@ in a cartesian space or a distance between two points in a cartesian space.</p>
 scalar
   : <loc href="#style-value-number">&lt;number&gt;</loc> units
 
-units
+<phrase><termdef id="defs-units" term=""><term>units</term></termdef></phrase>
   : "px"
   | "em"
   | "c"                                     // abbreviation of "cell"
@@ -16856,7 +16856,9 @@ determine (obtain) the computed style set <emph>CSS</emph> of
 <label>[compute containment scaling](<emph>inout</emph> target rectangle TR, <emph>in</emph> reference rectangle RR)</label>
 <def>
 <olist>
-  <item><p>It is <termref def="defs-considered-an-error">considered an error</termref> if the units of target rectangle TR and reference rectangle RR are not the same, in which case exit this procedure without modifying the target rectangle.</p></item>
+  <item><p>If the <termref def="defs-units">units</termref> of either target rectangle TR or reference rectangle RR are not expressed in
+  <termref def="defs-logical-pixel">logical pixels</termref>  (i.e., <code>px</code> units), then convert the units as required to
+  <termref def="defs-logical-pixel">logical pixels</termref>.</p></item>
   <item><p>If the width of the target rectangle TR, <emph>W<sub>t</sub></emph>&thinsp;, is zero, then set <emph>W<sub>t</sub></emph> to one;
   likewise, if the height of the target rectangle TR, <emph>H<sub>t</sub></emph>&thinsp;, is zero, then set <emph>H<sub>t</sub></emph> to one.</p></item>
   <item><p>Let <emph>SAR<sub>r</sub></emph> be the storage aspect ratio of the reference rectangle <emph>RR</emph>.</p></item>
@@ -16894,7 +16896,9 @@ determine (obtain) the computed style set <emph>CSS</emph> of
 <label>[compute cover scaling](<emph>inout</emph> target rectangle TR, <emph>in</emph> reference rectangle RR)</label>
 <def>
 <olist>
-  <item><p>It is <termref def="defs-considered-an-error">considered an error</termref> if the units of target rectangle TR and reference rectangle RR are not the same, in which case exit this procedure without modifying the target rectangle.</p></item>
+  <item><p>If the <termref def="defs-units">units</termref> of either target rectangle TR or reference rectangle RR are not expressed in
+  <termref def="defs-logical-pixel">logical pixels</termref>  (i.e., <code>px</code> units), then convert the units as required to
+  <termref def="defs-logical-pixel">logical pixels</termref>.</p></item>
   <item><p>If the width of the target rectangle TR, <emph>W<sub>t</sub></emph>&thinsp;, is zero, then set <emph>W<sub>t</sub></emph> to one;
   likewise, if the height of the target rectangle TR, <emph>H<sub>t</sub></emph>&thinsp;, is zero, then set <emph>H<sub>t</sub></emph> to one.</p></item>
   <item><p>Let <emph>SF<sub>W </sub> </emph> be <emph>W<sub>R</sub> </emph>/<emph>W<sub>T</sub> </emph>, where