Added a duplicate attribute present member to element

Author: andypaicu

dom.bs

@@ -5891,8 +5891,9 @@ dictionary ShadowRootInit {
 <dfn export id=concept-element-local-name for=Element>local name</dfn>,
 <dfn export id=concept-element-custom-element-state for=Element>custom element state</dfn>,
 <dfn export id=concept-element-custom-element-definition for=Element>custom element definition</dfn>,
-<dfn export id=concept-element-is-value for=Element><code>is</code> value</dfn>. When an
-<a for="/">element</a> is <a lt="create an element">created</a>, all of these values are
+<dfn export id=concept-element-is-value for=Element><code>is</code> value</dfn>, and
+<dfn export id=concept-element-duplicate-attribute-present for=Element>duplicate attribute present</dfn>.
+When an <a for="/">element</a> is <a lt="create an element">created</a>, all of these values are
 initialized.
 
 <p>An <a for=/>element</a>'s <a for=Element>custom element state</a> is one of
@@ -5973,13 +5974,17 @@ value of these steps:
 <p>To
 <dfn export id=concept-create-element lt="create an element|creating an element">create an element</dfn>,
 given a <var>document</var>, <var>localName</var>, <var>namespace</var>, and optional
-<var>prefix</var>, <var>is</var>, and <var>synchronous custom elements flag</var>, run these steps:
+<var>prefix</var>, <var>is</var>, <var>duplicate attribute present</var>, and
+<var>synchronous custom elements flag</var> run these steps:
 
 <ol>
  <li><p>If <var>prefix</var> was not given, let <var>prefix</var> be null.
 
  <li><p>If <var>is</var> was not given, let <var>is</var> be null.
 
+ <li><p>If <var>duplicate attribute present</var> was not given, let
+ <var>duplicate attribute present</var> be false.
+
  <li><p>Let <var>result</var> be null.
 
  <li><p>Let <var>definition</var> be the result of
@@ -6001,8 +6006,9 @@ given a <var>document</var>, <var>localName</var>, <var>namespace</var>, and opt
    <a for=Element>namespace prefix</a> set to <var>prefix</var>, <a for=Element>local name</a> set
    to <var>localName</var>, <a for=Element>custom element state</a> set to "<code>undefined</code>",
    <a for=Element>custom element definition</a> set to null,
-   <a for=Element><code>is</code> value</a> set to <var>is</var>, and <a for=Node>node document</a> set to
-   <var>document</var>.
+   <a for=Element><code>is</code> value</a> set to <var>is</var>, <a for=Node>node document</a> set to
+   <var>document</var>, and <a for=Element>duplicate attribute present</a> set to
+   <var>duplicate attribute present</var>.
 
    <li><p>If the <var>synchronous custom elements flag</var> is set,
    <a lt="upgrade an element">upgrade</a> <var>element</var> using <var>definition</var>.
@@ -6071,6 +6077,9 @@ given a <var>document</var>, <var>localName</var>, <var>namespace</var>, and opt
      <li><p>Set <var>result</var>'s <a for=Element>namespace prefix</a> to <var>prefix</var>.
 
      <li><p>Set <var>result</var>'s <a for=Element><code>is</code> value</a> to null.
+
+     <li><p>Set <var>result</var>'s <a for=Element>duplicate attribute present</a> to
+     <var>duplicate attribute present</var>.
     </ol>
 
     <p>If any of these steps threw an exception, then:</p>
@@ -6084,8 +6093,9 @@ given a <var>document</var>, <var>localName</var>, <var>namespace</var>, and opt
      <a for=Element>local name</a> set to <var>localName</var>,
      <a for=Element>custom element state</a> set to "<code>failed</code>",
      <a for=Element>custom element definition</a> set to null,
-     <a for=Element><code>is</code> value</a> set to null, and <a for=Node>node document</a> set to
-     <var>document</var>.
+     <a for=Element><code>is</code> value</a> set to null, <a for=Node>node document</a> set to
+     <var>document</var>, and <a for=Element>duplicate attribute present</a> set to
+     <var>duplicate attribute present</var>.
     </ol>
    </li>
 
@@ -6098,8 +6108,9 @@ given a <var>document</var>, <var>localName</var>, <var>namespace</var>, and opt
      <a for=Element>namespace prefix</a> set to <var>prefix</var>, <a for=Element>local name</a> set
      to <var>localName</var>, <a for=Element>custom element state</a> set to
      "<code>undefined</code>", <a for=Element>custom element definition</a> set to null,
-     <a for=Element><code>is</code> value</a> set to null, and <a for=Node>node document</a> set to
-     <var>document</var>.
+     <a for=Element><code>is</code> value</a> set to null, <a for=Node>node document</a> set to
+     <var>document</var>, and <a for=Element>duplicate attribute present</a> set to
+     <var>duplicate attribute present</var>.
 
      <li><p><a>Enqueue a custom element upgrade reaction</a> given <var>result</var> and
      <var>definition</var>.
@@ -6120,8 +6131,9 @@ given a <var>document</var>, <var>localName</var>, <var>namespace</var>, and opt
    <a for=Element>namespace prefix</a> set to <var>prefix</var>, <a for=Element>local name</a> set
    to <var>localName</var>, <a for=Element>custom element state</a> set to
    "<code>uncustomized</code>", <a for=Element>custom element definition</a> set to null,
-   <a for=Element><code>is</code> value</a> set to <var>is</var>, and <a for=Node>node document</a> set to
-   <var>document</var>.
+   <a for=Element><code>is</code> value</a> set to <var>is</var>,<a for=Node>node document</a> set to
+   <var>document</var>, and <a for=Element>duplicate attribute present</a> set to
+   <var>duplicate attribute present</var>.
 
    <li><p>If <var>namespace</var> is the <a>HTML namespace</a>, and either <var>localName</var> is a
    <a>valid custom element name</a> or <var>is</var> is non-null, then set <var>result</var>'s
@@ -9959,6 +9971,7 @@ Adrian Bateman,
 Aleksey Shvayka,
 Alex Komoroske,
 Alex Russell,
+Andy Paicu,
 Anthony Ramine,
 Arkadiusz Michalski,
 Arnaud Le Hors,