[cssom] add property priority to declaration block serialization rules

Author: skynavga

cssom/Overview.html

@@ -1874,11 +1874,18 @@ <h3 id="css-declaration-blocks"><span class="secno">6.5 </span>CSS Declaration B
           <ol>
             <li><p>If <var>s</var> is not empty, then append a SPACE (U+0020) to <var>s</var>.</li>
             <li><p>Append <var>n</var> to <var>s</var>.</li>
-            <li><p>Append COLON (U+003A) followed by SPACE (U+0020, i.e., "<code>: </code>", to <var>s</var>.</li>
+            <li><p>Append COLON (U+003A) followed by SPACE (U+0020), i.e., "<code>: </code>", to <var>s</var>.</li>
             <li><p>Append <var>v</var> to <var>s</var>.</li>
-            <li><p>Append SEMICOLON (U+003B), i.e., "<code>;</code>", to <var>s</var>.</li>
           </ol>
       </li>
+      <li><p>Let <var>p</var> be the value returned by <code><var>d</var>.getPropertyPriority(<var>n</var>)</code>.</li>
+      <li><p>If <var>p</var> is not the empty string, then perform the following sub-steps:</p>
+          <ol>
+            <li><p>Append SPACE (U+0020) followed by EXCLAMATION MARK (U+0021), i.e., "<code> !</code>", to <var>s</var>.</li>
+            <li><p>Append <var>p</var> to <var>s</var>.</li>
+          </ol>
+      </li>
+      <li><p>Append SEMICOLON (U+003B), i.e., "<code>;</code>", to <var>s</var>.</li>
     </ol>
     </li>
     <li><p>Return <var>s</var>.</li>

cssom/cssom-source

@@ -1478,11 +1478,18 @@
           <ol>
             <li><p>If <var>s</var> is not empty, then append a SPACE (U+0020) to <var>s</var>.</p></li>
             <li><p>Append <var>n</var> to <var>s</var>.</p></li>
-            <li><p>Append COLON (U+003A) followed by SPACE (U+0020, i.e., "<code>: </code>", to <var>s</var>.</p></li>
+            <li><p>Append COLON (U+003A) followed by SPACE (U+0020), i.e., "<code>: </code>", to <var>s</var>.</p></li>
             <li><p>Append <var>v</var> to <var>s</var>.</p></li>
-            <li><p>Append SEMICOLON (U+003B), i.e., "<code>;</code>", to <var>s</var>.</p></li>
           </ol>
       </li>
+      <li><p>Let <var>p</var> be the value returned by <code><var>d</var>.getPropertyPriority(<var>n</var>)</code>.</p></li>
+      <li><p>If <var>p</var> is not the empty string, then perform the following sub-steps:</p>
+          <ol>
+            <li><p>Append SPACE (U+0020) followed by EXCLAMATION MARK (U+0021), i.e., "<code> !</code>", to <var>s</var>.</p></li>
+            <li><p>Append <var>p</var> to <var>s</var>.</p></li>
+          </ol>
+      </li>
+      <li><p>Append SEMICOLON (U+003B), i.e., "<code>;</code>", to <var>s</var>.</p></li>
     </ol>
     </li>
     <li><p>Return <var>s</var>.</p></li>