Fix setMatrixValue("none")

Part of #55.

Author: zcorpan

geometry/Overview.bs

@@ -1185,15 +1185,17 @@ Note: Authors who use chained method calls are recommended to use mutable transf
   <dt><dfn>setMatrixValue(<var>transformList</var>)</dfn></dt>
   <dd>
     <ol>
-      <li>If <var>transformList</var> is the empty string, set it to the string "<code lt>matrix(1,
-      0, 0, 1, 0, 0)</code>".</li>
-      <li>Parse <var>transformList</var> by following the syntax description in “<a
-      href=https://drafts.csswg.org/css-transforms-1/#svg-syntax>Syntax of the SVG ‘transform’
-      attribute</a>” [[!CSS3-TRANSFORMS]] to a <<transform-list>>. If parsing is not successful, or
-      any <<transform-function>> has <<length>> values without <a spec='css-values'>absolute
-      length</a> units<!--For WD: <a spec='css-values-3'>absolute length units</a>-->, or any
-      keyword other than ''transform/none'' is used, throw a {{SyntaxError}}
-      exception.</li>
+      <li>If <var>transformList</var> is the empty string, set it to the string "<code>matrix(1, 0,
+      0, 1, 0, 0)</code>".</li>
+      <li>Parse <var>transformList</var> into <var>parsedValue</var> by following the syntax
+      description in “<a href=https://drafts.csswg.org/css-transforms-1/#svg-syntax>Syntax of the
+      SVG ‘transform’ attribute</a>” [[!CSS3-TRANSFORMS]] to a <<transform-list>> or the keyword
+      ''transform/none''. If parsing is not successful, or any <<transform-function>> has <<length>>
+      values without <a spec='css-values'>absolute length</a> units<!--For WD: <a
+      spec='css-values-3'>absolute length units</a>-->, or any keyword other than ''transform/none''
+      is used, throw a {{SyntaxError}} exception.</li>
+      <li>If <var>parsedValue</var> is ''transform/none'', set <var>parsedValue</var> to a
+      <<transform-list>> containing a single identity matrix</li>
       <li>Set <a>is2D</a> to <code>false</code> if the <<transform-list>> consists of any <a href='https://drafts.csswg.org/css-transforms-1/#three-d-transform-functions'>3D Transform functions</a>. Otherwise set <a>is2D</a> to <code>true</code>.</li>
       <li>Transform all <<transform-function>>s to 4x4 matrices by following the “<a href=https://drafts.csswg.org/css-transforms-1/#mathematical-description>Mathematical Description of Transform Functions</a>” [[!CSS3-TRANSFORMS]].</li>
       <li>Post-multiply all matrices from left to right to a combined 4x4 matrix.</li>