[geometry] Editorial: simplify 'validate and fixup' algorithm

Fixes https://www.w3.org/Bugs/Public/show_bug.cgi?id=29820

geometry/Overview.bs

@@ -21,7 +21,7 @@ Abstract: This specification provides basic geometric interfaces to represent po
 !Issues list: <a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=FXTF&amp;component=Geometry&amp;resolution=---">Bugzilla</a> (<a href="https://www.w3.org/Bugs/Public/enter_bug.cgi?product=FXTF&amp;component=Geometry">file a bug</a>)
 Test Suite: http://test.csswg.org/suites/geometry-1_dev/nightly-unstable/
 Use <i> Autolinks: yes
-Ignored Vars: f, Point object, m44, e, m42, quad1, m41, stringifier, point object, m12, c, transformPoint, m21, d, m22, quad2, sz
+Ignored Vars: a, b, f, Point object, m44, e, m42, quad1, m41, stringifier, point object, m12, c, transformPoint, m21, d, m22, quad2, sz
 </pre>
 
 <pre class=anchors>
@@ -636,12 +636,12 @@ To <dfn>validate and fixup</dfn> a {{DOMMatrixInit}} dictionary <var>dict</var>,
       or at least one of {{DOMMatrixInit/m33}}, {{DOMMatrixInit/m44}}
       are present with a value other than ''1''.
     </ul>
-  <li><a>Set the dictionary members</a> {{DOMMatrixInit/a}} and {{DOMMatrixInit/m11}} with fallback value ''1''.
-  <li><a>Set the dictionary members</a> {{DOMMatrixInit/b}} and {{DOMMatrixInit/m12}} with fallback value ''0''.
-  <li><a>Set the dictionary members</a> {{DOMMatrixInit/c}} and {{DOMMatrixInit/m21}} with fallback value ''0''.
-  <li><a>Set the dictionary members</a> {{DOMMatrixInit/d}} and {{DOMMatrixInit/m22}} with fallback value ''1''.
-  <li><a>Set the dictionary members</a> {{DOMMatrixInit/e}} and {{DOMMatrixInit/m41}} with fallback value ''0''.
-  <li><a>Set the dictionary members</a> {{DOMMatrixInit/f}} and {{DOMMatrixInit/m42}} with fallback value ''0''.
+  <li>If {{DOMMatrixInit/m11}} is not present then set it to the value of member {{DOMMatrixInit/a}}, or value ''1'' if {{DOMMatrixInit/a}} is also not present.
+  <li>If {{DOMMatrixInit/m12}} is not present then set it to the value of member {{DOMMatrixInit/b}}, or value ''0'' if {{DOMMatrixInit/b}} is also not present.
+  <li>If {{DOMMatrixInit/m21}} is not present then set it to the value of member {{DOMMatrixInit/c}}, or value ''0'' if {{DOMMatrixInit/c}} is also not present.
+  <li>If {{DOMMatrixInit/m22}} is not present then set it to the value of member {{DOMMatrixInit/d}}, or value ''1'' if {{DOMMatrixInit/d}} is also not present.
+  <li>If {{DOMMatrixInit/m41}} is not present then set it to the value of member {{DOMMatrixInit/e}}, or value ''0'' if {{DOMMatrixInit/e}} is also not present.
+  <li>If {{DOMMatrixInit/m42}} is not present then set it to the value of member {{DOMMatrixInit/f}}, or value ''0'' if {{DOMMatrixInit/f}} is also not present.
   <li>If {{DOMMatrixInit/is2D}} is not present and at least one of
   {{DOMMatrixInit/m31}}, {{DOMMatrixInit/m32}}, {{DOMMatrixInit/m13}}, {{DOMMatrixInit/m23}},
   {{DOMMatrixInit/m43}}, {{DOMMatrixInit/m14}}, {{DOMMatrixInit/m24}}, {{DOMMatrixInit/m34}}
@@ -657,14 +657,6 @@ are the same if they have identical IEEE 754 double-precision bit patterns.
 
 Note: This means that two ''NaN'' values are the same.
 
-To <dfn>set the dictionary members</dfn> <var>a</var> and <var>b</var> of a {{DOMMatrixInit}} dictionary, with a fallback value <var>fallback</var>, run the following steps:
-
-<ol>
-  <li>If <var>a</var> is present and <var>b</var> is not present, set the <var>b</var> dictionary member to the value of <var>a</var>.
-  <li>Otherwise, if <var>b</var> is present and <var>a</var> is not present, set the <var>a</var> dictionary member to the value of <var>b</var>.
-  <li>Otherwise, if neither <var>a</var> or <var>b</var> are present, set <var>a</var> and <var>b</var> dictionary members to <var>fallback</var>.
-</ol>
-
 <h3 id='dommatrix-create'>Creating DOMMatrixReadOnly and DOMMatrix objects</h3>
 
 To <dfn>create a 2d matrix</dfn> of type <var>type</var> being either {{DOMMatrixReadOnly}} or {{DOMMatrix}},