Change 'auto' value of 'mask-mode' to 'match-source' as resolved in CSS/SVG meeting about 25 minutes ago.

This addresses the issue raised in:
https://lists.w3.org/Archives/Public/public-fx/2015OctDec/0021.html

Author: dbaron

css-masking-1/Overview.html

@@ -529,7 +529,7 @@ <h3 class="heading settled" data-level="7.2" id="the-mask-mode"><span class="sec
       <td class="prod"><a class="production css" data-link-type="type" href="#typedef-masking-mode">&lt;masking-mode></a><a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#mult-comma">#</a>
      <tr>
       <th>Initial:
-      <td>auto
+      <td>match-source
      <tr>
       <th>Applies to:
       <td>All elements. In SVG, it applies to <a href="https://www.w3.org/TR/2011/REC-SVG11-20110816/intro.html#TermContainerElement">container elements</a> excluding the <a href="https://www.w3.org/TR/2011/REC-SVG11-20110816/struct.html#DefsElement"><code class="element-name">&lt;defs></code></a> element and all <a href="https://www.w3.org/TR/2011/REC-SVG11-20110816/intro.html#TermGraphicsElement">graphics elements</a>
@@ -550,14 +550,14 @@ <h3 class="heading settled" data-level="7.2" id="the-mask-mode"><span class="sec
       <td>no
    </table>
    <p>The <a class="property" data-link-type="propdesc" href="#propdef-mask-mode">mask-mode</a> property indicates whether the <a class="production css" data-link-type="type" href="#typedef-mask-reference">&lt;mask-reference></a> is treated as luminance mask or alpha mask. (See <a href="#MaskValues">Mask processing</a>.)</p>
-<pre class="prod"><dfn data-dfn-type="type" data-export="" id="typedef-masking-mode">&lt;masking-mode><a class="self-link" href="#typedef-masking-mode"></a></dfn> = alpha <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> luminance <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> auto</pre>
+<pre class="prod"><dfn data-dfn-type="type" data-export="" id="typedef-masking-mode">&lt;masking-mode><a class="self-link" href="#typedef-masking-mode"></a></dfn> = alpha <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> luminance <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-3/#comb-one">|</a> match-source</pre>
    <p>Values have the following meanings:</p>
    <dl>
     <dt><dfn class="css" data-dfn-for="mask-mode" data-dfn-type="value" data-export="" id="valdef-mask-mode-alpha">alpha<a class="self-link" href="#valdef-mask-mode-alpha"></a></dfn>
     <dd> A value of <a class="css" data-link-type="value" href="#valdef-mask-mode-alpha">alpha</a> indicates that the alpha values of the <a data-link-type="dfn" href="#mask-layer-image">mask layer image</a> should be used as the mask values. See <a href="#MaskValues">Calculating mask values</a>. 
     <dt><dfn class="css" data-dfn-for="mask-mode" data-dfn-type="value" data-export="" id="valdef-mask-mode-luminance">luminance<a class="self-link" href="#valdef-mask-mode-luminance"></a></dfn>
     <dd> A value of <a class="css" data-link-type="value" href="#valdef-mask-mode-luminance">luminance</a> indicates that the luminance values of the <a data-link-type="dfn" href="#mask-layer-image">mask layer image</a> should be used as the mask values. See <a href="#MaskValues">Calculating mask values</a>. 
-    <dt><dfn class="css" data-dfn-for="mask-mode" data-dfn-type="value" data-export="" id="valdef-mask-mode-auto">auto<a class="self-link" href="#valdef-mask-mode-auto"></a></dfn>
+    <dt><dfn class="css" data-dfn-for="mask-mode" data-dfn-type="value" data-export="" id="valdef-mask-mode-match-source">match-source<a class="self-link" href="#valdef-mask-mode-match-source"></a></dfn>
     <dd>
      <p>If the <a class="production css" data-link-type="type" href="#typedef-mask-reference">&lt;mask-reference></a> of the <a class="property" data-link-type="propdesc" href="#propdef-mask-image">mask-image</a> property is of type <a class="production css" data-link-type="type" href="#typedef-mask-source">&lt;mask-source></a> the luminance values of the <a data-link-type="dfn" href="#mask-layer-image">mask layer image</a> should be used as the mask values.</p>
      <p>If the <a class="production css" data-link-type="type" href="#typedef-mask-reference">&lt;mask-reference></a> of the <a class="property" data-link-type="propdesc" href="#propdef-mask-image">mask-image</a> property is of type <a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-images-3/#typedef-image">&lt;image></a> the alpha values of the <a data-link-type="dfn" href="#mask-layer-image">mask layer image</a> should be used as the mask values.</p>
@@ -1417,10 +1417,10 @@ <h3 class="heading settled" data-level="9.2" id="the-mask-type"><span class="sec
     <dt><dfn class="css" data-dfn-for="mask-type" data-dfn-type="value" data-export="" id="valdef-mask-type-alpha">alpha<a class="self-link" href="#valdef-mask-type-alpha"></a></dfn>
     <dd> Indicates that the alpha values of the mask should be used. 
    </dl>
-   <p>The <a class="property" data-link-type="propdesc" href="#propdef-mask-type">mask-type</a> property allows the author of the <a data-link-type="element" href="#elementdef-mask">mask</a> element to specify the preferred masking mode. However, the author can override this preference by setting the <a class="property" data-link-type="propdesc" href="#propdef-mask-mode">mask-mode</a> value to something different than <a class="css" data-link-type="maybe" href="#valdef-mask-mode-auto">auto</a> on the masked content.</p>
-   <div class="example" id="example-c033a63a">
-    <a class="self-link" href="#example-c033a63a"></a> 
-    <p>In the following example the computed value of <a class="property" data-link-type="propdesc" href="#propdef-mask-type">mask-type</a> is <a class="css" data-link-type="value" href="#valdef-mask-type-luminance">luminance</a> and the computed value of <a class="property" data-link-type="propdesc" href="#propdef-mask-mode">mask-mode</a> is <a class="css" data-link-type="maybe" href="#valdef-mask-mode-auto">auto</a>. The UA must follow the preferred masking mode defined on the <a data-link-type="element" href="#elementdef-mask">mask</a> element. </p>
+   <p>The <a class="property" data-link-type="propdesc" href="#propdef-mask-type">mask-type</a> property allows the author of the <a data-link-type="element" href="#elementdef-mask">mask</a> element to specify the preferred masking mode. However, the author can override this preference by setting the <a class="property" data-link-type="propdesc" href="#propdef-mask-mode">mask-mode</a> value to something different than <a class="css" data-link-type="maybe" href="#valdef-mask-mode-match-source">match-source</a> on the masked content.</p>
+   <div class="example" id="example-2f49b58e">
+    <a class="self-link" href="#example-2f49b58e"></a> 
+    <p>In the following example the computed value of <a class="property" data-link-type="propdesc" href="#propdef-mask-type">mask-type</a> is <a class="css" data-link-type="value" href="#valdef-mask-type-luminance">luminance</a> and the computed value of <a class="property" data-link-type="propdesc" href="#propdef-mask-mode">mask-mode</a> is <a class="css" data-link-type="maybe" href="#valdef-mask-mode-match-source">match-source</a>. The UA must follow the preferred masking mode defined on the <a data-link-type="element" href="#elementdef-mask">mask</a> element. </p>
 <pre><code class="html">&lt;svg>
   &lt;mask style="mask-type: luminance;" id="mask">
     ...
@@ -1488,8 +1488,8 @@ <h2 class="no-num heading settled" id="clip-property"><span class="content">Appe
     <dt><dfn class="css" data-dfn-type="function" data-export="" id="funcdef-rect">rect()<a class="self-link" href="#funcdef-rect"></a></dfn> = rect( <a class="production css" data-link-type="type" href="#typedef-top">&lt;top></a>, <a class="production css" data-link-type="type" href="#typedef-right">&lt;right></a>, <a class="production css" data-link-type="type" href="#typedef-bottom">&lt;bottom></a>, <a class="production css" data-link-type="type" href="#typedef-left">&lt;left></a> )
     <dd>
      <p><a class="production css" data-link-type="type" href="#typedef-top">&lt;top></a> and <a class="production css" data-link-type="type" href="#typedef-bottom">&lt;bottom></a> specify offsets from the top border edge of the box, and <a class="production css" data-link-type="type" href="#typedef-right">&lt;right></a>, and <a class="production css" data-link-type="type" href="#typedef-left">&lt;left></a> specify offsets from the left border edge of the box. Authors should separate offset values with commas. User agents must support separation with commas, but may also support separation without commas (but not a combination), because a previous revision of this specification was ambiguous in this respect.</p>
-     <p><dfn class="css" data-dfn-type="type" data-export="" id="typedef-top">&lt;top><a class="self-link" href="#typedef-top"></a></dfn>, <dfn class="css" data-dfn-type="type" data-export="" id="typedef-right">&lt;right><a class="self-link" href="#typedef-right"></a></dfn>, <dfn class="css" data-dfn-type="type" data-export="" id="typedef-bottom">&lt;bottom><a class="self-link" href="#typedef-bottom"></a></dfn>, and <dfn class="css" data-dfn-type="type" data-export="" id="typedef-left">&lt;left><a class="self-link" href="#typedef-left"></a></dfn> may either have a <a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-values-3/#length-value">&lt;length></a> value or <a class="css" data-link-type="maybe" href="#valdef-mask-mode-auto">auto</a>. Negative lengths are permitted. The value <a class="css" data-link-type="maybe" href="#valdef-mask-mode-auto">auto</a> means that a given edge of the clipping region will be the same as the edge of the element’s generated border box (i.e., <a class="css" data-link-type="maybe" href="#valdef-mask-mode-auto">auto</a> means the same as <span class="css">0</span> for <a class="production css" data-link-type="type" href="#typedef-top">&lt;top></a> and <a class="production css" data-link-type="type" href="#typedef-left">&lt;left></a>, the same as the <a data-link-type="dfn" href="https://drafts.csswg.org/css-cascade-4/#used-value">used value</a> of the height plus the sum of vertical padding and border widths for <a class="production css" data-link-type="type" href="#typedef-bottom">&lt;bottom></a>, and the same as the used value of the width plus the sum of the horizontal padding and border widths for <a class="production css" data-link-type="type" href="#typedef-right">&lt;right></a>, such that four <a class="css" data-link-type="maybe" href="#valdef-mask-mode-auto">auto</a> values result in the clipping region being the same as the element’s border box).</p>
-     <p>When coordinates are rounded to pixel coordinates, care should be taken that no pixels remain visible when <a class="production css" data-link-type="type" href="#typedef-left">&lt;left></a> and <a class="production css" data-link-type="type" href="#typedef-right">&lt;right></a> have the same value (or <a class="production css" data-link-type="type" href="#typedef-top">&lt;top></a> and <a class="production css" data-link-type="type" href="#typedef-bottom">&lt;bottom></a> have the same value), and conversely that no pixels within the element’s border box remain hidden when these values are <a class="css" data-link-type="maybe" href="#valdef-mask-mode-auto">auto</a>.</p>
+     <p><dfn class="css" data-dfn-type="type" data-export="" id="typedef-top">&lt;top><a class="self-link" href="#typedef-top"></a></dfn>, <dfn class="css" data-dfn-type="type" data-export="" id="typedef-right">&lt;right><a class="self-link" href="#typedef-right"></a></dfn>, <dfn class="css" data-dfn-type="type" data-export="" id="typedef-bottom">&lt;bottom><a class="self-link" href="#typedef-bottom"></a></dfn>, and <dfn class="css" data-dfn-type="type" data-export="" id="typedef-left">&lt;left><a class="self-link" href="#typedef-left"></a></dfn> may either have a <a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-values-3/#length-value">&lt;length></a> value or <span class="css">auto</span>. Negative lengths are permitted. The value <span class="css">auto</span> means that a given edge of the clipping region will be the same as the edge of the element’s generated border box (i.e., <span class="css">auto</span> means the same as <span class="css">0</span> for <a class="production css" data-link-type="type" href="#typedef-top">&lt;top></a> and <a class="production css" data-link-type="type" href="#typedef-left">&lt;left></a>, the same as the <a data-link-type="dfn" href="https://drafts.csswg.org/css-cascade-4/#used-value">used value</a> of the height plus the sum of vertical padding and border widths for <a class="production css" data-link-type="type" href="#typedef-bottom">&lt;bottom></a>, and the same as the used value of the width plus the sum of the horizontal padding and border widths for <a class="production css" data-link-type="type" href="#typedef-right">&lt;right></a>, such that four <span class="css">auto</span> values result in the clipping region being the same as the element’s border box).</p>
+     <p>When coordinates are rounded to pixel coordinates, care should be taken that no pixels remain visible when <a class="production css" data-link-type="type" href="#typedef-left">&lt;left></a> and <a class="production css" data-link-type="type" href="#typedef-right">&lt;right></a> have the same value (or <a class="production css" data-link-type="type" href="#typedef-top">&lt;top></a> and <a class="production css" data-link-type="type" href="#typedef-bottom">&lt;bottom></a> have the same value), and conversely that no pixels within the element’s border box remain hidden when these values are <span class="css">auto</span>.</p>
    </dl>
    <div class="example" id="example-1722a1b1">
     <a class="self-link" href="#example-1722a1b1"></a> 
@@ -1754,7 +1754,6 @@ <h3 class="no-num heading settled" id="index-defined-here"><span class="content"
      <li><a href="#valdef-mask-border-mode-alpha">value for mask-border-mode</a><span>, in §8.2</span>
      <li><a href="#valdef-mask-type-alpha">value for mask-type</a><span>, in §9.2</span>
     </ul>
-   <li><a href="#valdef-mask-mode-auto">auto</a><span>, in §7.2</span>
    <li>
     border-box
     <ul>
@@ -1849,6 +1848,7 @@ <h3 class="no-num heading settled" id="index-defined-here"><span class="content"
    <li><a href="#typedef-mask-source">&lt;mask-source></a><span>, in §7.1</span>
    <li><a href="#propdef-mask-type">mask-type</a><span>, in §9.2</span>
    <li><a href="#element-attrdef-mask-maskunits">maskUnits</a><span>, in §9.1</span>
+   <li><a href="#valdef-mask-mode-match-source">match-source</a><span>, in §7.2</span>
    <li><a href="#valdef-mask-clip-no-clip">no-clip</a><span>, in §7.5</span>
    <li><a href="#valdef-clip-rule-nonzero">nonzero</a><span>, in §6.2</span>
    <li>
@@ -2212,7 +2212,7 @@ <h2 class="no-num heading settled" id="property-index"><span class="content">Pro
      <tr>
       <th scope="row"><a class="css" data-link-type="property" href="#propdef-mask-mode">mask-mode</a>
       <td>&lt;masking-mode>#
-      <td>auto
+      <td>match-source
       <td>All elements. In SVG, it applies to container elements excluding the &lt;defs> element and all graphics elements
       <td>no
       <td>n/a