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common-dom-interfaces.html 99.2 KB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html lang="en-US-x-Hixie" ><head><title>2.8 Common DOM interfaces &#8212; HTML5 </title><style type="text/css">
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   ul.domTree .t10 code { color: teal; }

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     margin: 0 auto 0 auto !important;
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requirements"><link href="http://www.w3.org/StyleSheets/TR/W3C-WD" rel="stylesheet" type="text/css"><style type="text/css">

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   .applies thead code { display: block; }
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   .apple-table-examples.e2 th[scope=row] { padding-left: 1em; }
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   .details-example img { vertical-align: top; }

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   <h1>HTML5</h1>
   </div><div>
   <a href="fetching-resources.html" class="prev">2.7 Fetching resources</a> &#8211;
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  <ol class="toc"><li><ol><li><a href="common-dom-interfaces.html#common-dom-interfaces"><span class="secno">2.8 </span>Common DOM interfaces</a>
    <ol><li><a href="common-dom-interfaces.html#reflecting-content-attributes-in-idl-attributes"><span class="secno">2.8.1 </span>Reflecting content attributes in IDL attributes</a></li><li><a href="common-dom-interfaces.html#collections-0"><span class="secno">2.8.2 </span>Collections</a>
      <ol><li><a href="common-dom-interfaces.html#htmlcollection-0"><span class="secno">2.8.2.1 </span>HTMLCollection</a></li><li><a href="common-dom-interfaces.html#htmlallcollection-0"><span class="secno">2.8.2.2 </span>HTMLAllCollection</a></li><li><a href="common-dom-interfaces.html#htmlformcontrolscollection-0"><span class="secno">2.8.2.3 </span>HTMLFormControlsCollection</a></li><li><a href="common-dom-interfaces.html#htmloptionscollection-0"><span class="secno">2.8.2.4 </span>HTMLOptionsCollection</a></li></ol></li><li><a href="common-dom-interfaces.html#domtokenlist-0"><span class="secno">2.8.3 </span>DOMTokenList</a></li><li><a href="common-dom-interfaces.html#domsettabletokenlist-0"><span class="secno">2.8.4 </span>DOMSettableTokenList</a></li><li><a href="common-dom-interfaces.html#safe-passing-of-structured-data"><span class="secno">2.8.5 </span>Safe passing of structured data</a></li><li><a href="common-dom-interfaces.html#domstringmap-0"><span class="secno">2.8.6 </span>DOMStringMap</a></li><li><a href="common-dom-interfaces.html#dom-feature-strings"><span class="secno">2.8.7 </span>DOM feature strings</a></li><li><a href="common-dom-interfaces.html#exceptions"><span class="secno">2.8.8 </span>Exceptions</a></li><li><a href="common-dom-interfaces.html#garbage-collection"><span class="secno">2.8.9 </span>Garbage collection</a></li></ol></li></ol></li></ol></div>

  <h3 id="common-dom-interfaces"><span class="secno">2.8 </span>Common DOM interfaces</h3><h4 id="reflecting-content-attributes-in-idl-attributes"><span class="secno">2.8.1 </span>Reflecting content attributes in IDL attributes</h4><p>Some IDL attributes are defined to <dfn id="reflect">reflect</dfn> a
  particular content attribute. This means that on getting, the IDL
  attribute returns the current value of the content attribute, and on
  setting, the IDL attribute changes the value of the content
  attribute to the given value.</p><div class="impl">

  <p>In general, on getting, if the content attribute is not present,
  the IDL attribute must act as if the content attribute's value is
  the empty string; and on setting, if the content attribute is not
  present, it must first be added.</p>

  <p>If a reflecting IDL attribute is a <code>DOMString</code>
  attribute whose content attribute is defined to contain a
  <a href="urls.html#url">URL</a>, then on getting, the IDL attribute must <a href="urls.html#resolve-a-url" title="resolve a url">resolve</a> the value of the content
  attribute relative to the element and return the resulting
  <a href="urls.html#absolute-url">absolute URL</a> if that was successful, or the empty
  string otherwise; and on setting, must set the content attribute to
  the specified literal value. If the content attribute is absent, the
  IDL attribute must return the default value, if the content
  attribute has one, or else the empty string.</p>

  <p>If a reflecting IDL attribute is a <code>DOMString</code>
  attribute whose content attribute is defined to contain one or more
  <a href="urls.html#url" title="URL">URLs</a>, then on getting, the IDL attribute
  must <a href="common-microsyntaxes.html#split-a-string-on-spaces" title="split a string on spaces">split the content
  attribute on spaces</a> and return the concatenation of <a href="urls.html#resolve-a-url" title="resolve a URL">resolving</a> each token URL to an
  <a href="urls.html#absolute-url">absolute URL</a> relative to the element, with a single
  U+0020 SPACE character between each URL, ignoring any tokens that
  did not resolve successfully. If the content attribute is absent,
  the IDL attribute must return the default value, if the content
  attribute has one, or else the empty string. On setting, the IDL
  attribute must set the content attribute to the specified literal
  value.</p>

  <p>If a reflecting IDL attribute is a <code>DOMString</code>
  attribute whose content attribute is an <a href="common-microsyntaxes.html#enumerated-attribute">enumerated
  attribute</a>, and the IDL attribute is <dfn id="limited-to-only-known-values">limited to only
  known values</dfn>, then, on getting, the IDL attribute must return
  the conforming value associated with the state the attribute is in
  (in its canonical case), or the empty string if the attribute is in
  a state that has no associated keyword value; and on setting, the
  content attribute must be set to the specified new value.</p>

  <p>If a reflecting IDL attribute is a <code>DOMString</code>
  attribute but doesn't fall into any of the above categories, then
  the getting and setting must be done in a transparent,
  case-preserving manner.</p>

  <p>If a reflecting IDL attribute is a <code title="">boolean</code>
  attribute, then on getting the IDL attribute must return true if the
  content attribute is set, and false if it is absent. On setting, the
  content attribute must be removed if the IDL attribute is set to
  false, and must be set to the empty string if the IDL attribute is
  set to true. (This corresponds to the rules for <a href="common-microsyntaxes.html#boolean-attribute" title="boolean
  attribute">boolean content attributes</a>.)</p>

  <p>If a reflecting IDL attribute has a signed integer type
  (<code>long</code>) then, on getting, the content attribute must be
  parsed according to the <a href="common-microsyntaxes.html#rules-for-parsing-integers" title="rules for parsing
  integers">rules for parsing signed integers</a>, and if that is
  successful, and the value is in the range of the IDL attribute's
  type, the resulting value must be returned. If, on the other hand,
  it fails or returns an out of range value, or if the attribute is
  absent, then the default value must be returned instead, or 0 if
  there is no default value. On setting, the given value must be
  converted to the shortest possible string representing the number as
  a <a href="common-microsyntaxes.html#valid-integer">valid integer</a> and then that string must be used as
  the new content attribute value.</p>

  <p>If a reflecting IDL attribute has a signed integer type
  (<code>long</code>) that is <dfn id="limited-to-only-non-negative-numbers">limited to only non-negative
  numbers</dfn> then, on getting, the content attribute must be parsed
  according to the <a href="common-microsyntaxes.html#rules-for-parsing-non-negative-integers">rules for parsing non-negative
  integers</a>, and if that is successful, and the value is in the
  range of the IDL attribute's type, the resulting value must be
  returned. If, on the other hand, it fails or returns an out of range
  value, or if the attribute is absent, the default value must be
  returned instead, or &#8722;1 if there is no default value. On
  setting, if the value is negative, the user agent must fire an
  <code><a href="#index_size_err">INDEX_SIZE_ERR</a></code> exception. Otherwise, the given value
  must be converted to the shortest possible string representing the
  number as a <a href="common-microsyntaxes.html#valid-non-negative-integer">valid non-negative integer</a> and then that
  string must be used as the new content attribute value.</p>

  <p>If a reflecting IDL attribute has an <em>unsigned</em> integer
  type (<code>unsigned long</code>) then, on getting, the content
  attribute must be parsed according to the <a href="common-microsyntaxes.html#rules-for-parsing-non-negative-integers">rules for parsing
  non-negative integers</a>, and if that is successful, and the
  value is in the range 0 to 2147483647 inclusive, the resulting value
  must be returned. If, on the other hand, it fails or returns an out
  of range value, or if the attribute is absent, the default value
  must be returned instead, or 0 if there is no default value. On
  setting, the given value must be converted to the shortest possible
  string representing the number as a <a href="common-microsyntaxes.html#valid-non-negative-integer">valid non-negative
  integer</a> and then that string must be used as the new content
  attribute value.</p>
  
  <p>If a reflecting IDL attribute has an unsigned integer type
  (<code>unsigned long</code>) that is <dfn id="limited-to-only-non-negative-numbers-greater-than-zero">limited to only
  non-negative numbers greater than zero</dfn>, then the behavior is
  similar to the previous case, but zero is not allowed. On getting,
  the content attribute must first be parsed according to the
  <a href="common-microsyntaxes.html#rules-for-parsing-non-negative-integers">rules for parsing non-negative integers</a>, and if that is
  successful, and the value is in the range 1 to 2147483647 inclusive,
  the resulting value must be returned. If, on the other hand, it
  fails or returns an out of range value, or if the attribute is
  absent, the default value must be returned instead, or 1 if there is
  no default value. On setting, if the value is zero, the user agent
  must fire an <code><a href="#index_size_err">INDEX_SIZE_ERR</a></code> exception. Otherwise, the
  given value must be converted to the shortest possible string
  representing the number as a <a href="common-microsyntaxes.html#valid-non-negative-integer">valid non-negative integer</a>
  and then that string must be used as the new content attribute
  value.</p> 

  <p>If a reflecting IDL attribute has a floating point number type
  (<code>double</code>), then, on getting, the content attribute must
  be parsed according to the <a href="common-microsyntaxes.html#rules-for-parsing-floating-point-number-values">rules for parsing floating point
  number values</a>, and if that is successful, the resulting value
  must be returned. If, on the other hand, it fails, or if the
  attribute is absent, the default value must be returned instead, or
  0.0 if there is no default value. On setting, the given value must
  be converted to the <a href="common-microsyntaxes.html#best-representation-of-the-number-as-a-floating-point-number">best representation of the number as a
  floating point number</a> and then that string must be used as
  the new content attribute value.</p>

  <p class="note">The values Infinity and Not-a-Number (NaN) values
  throw an exception on setting, as <a href="infrastructure.html#float-nan">defined
  earlier</a>.</p>

  <p>If a reflecting IDL attribute has the type
  <code><a href="#domtokenlist">DOMTokenList</a></code> or <code><a href="#domsettabletokenlist">DOMSettableTokenList</a></code>, then
  on getting it must return a <code><a href="#domtokenlist">DOMTokenList</a></code> or
  <code><a href="#domsettabletokenlist">DOMSettableTokenList</a></code> object (as appropriate) whose
  underlying string is the element's corresponding content attribute.
  When the object mutates its underlying string, the content attribute
  must itself be immediately mutated. When the attribute is absent,
  then the string represented by the object is the empty string; when
  the object mutates this empty string, the user agent must add the
  corresponding content attribute, with its value set to the value it
  would have been set to after mutating the empty string. The same
  <code><a href="#domtokenlist">DOMTokenList</a></code> or <code><a href="#domsettabletokenlist">DOMSettableTokenList</a></code>
  object must be returned every time for each attribute.</p>

  <div class="example">

   <p>If an element with no attributes has its <code title="dom-tokenlist-remove"><a href="#dom-tokenlist-remove">element.classList.remove()</a></code>
   method invoked, the underlying string won't be changed, since the
   result of removing any token from the empty string is still the
   empty string. However, if the <code title="dom-tokenlist-add"><a href="#dom-tokenlist-add">element.classList.add()</a></code> method is
   then invoked, a <code title="attr-class"><a href="elements.html#classes">class</a></code> attribute
   will be added to the element with the value of the token to be
   added.</p>

  </div>

  <p>If a reflecting IDL attribute has the type
  <code><a href="elements.html#htmlelement">HTMLElement</a></code>, or an interface that descends from
  <code><a href="elements.html#htmlelement">HTMLElement</a></code>, then, on getting, it must run the
  following algorithm (stopping at the first point where a value is
  returned):</p>

  <ol><li>If the corresponding content attribute is absent, then the
   IDL attribute must return null.</li>

   <li>Let <var title="">candidate</var> be the element that the <code title="dom-Document-getElementById"><a href="infrastructure.html#dom-document-getelementbyid">document.getElementById()</a></code> method
   would find when called on the content attribute's document if it
   was passed as its argument the current value of the corresponding
   content attribute.</li>

   <li>If <var title="">candidate</var> is null, or if it is not
   type-compatible with the IDL attribute, then the IDL attribute must
   return null.</li>

   <li>Otherwise, it must return <var title="">candidate</var>.</li>

  </ol><p>On setting, if the given element has an <code title="attr-id"><a href="elements.html#the-id-attribute">id</a></code> attribute, then the content attribute must
  be set to the value of that <code title="attr-id"><a href="elements.html#the-id-attribute">id</a></code>
  attribute. Otherwise, the IDL attribute must be set to the empty
  string.</p>

  </div><h4 id="collections-0"><span class="secno">2.8.2 </span>Collections</h4><p>The <code><a href="#htmlcollection">HTMLCollection</a></code>, <code><a href="#htmlallcollection">HTMLAllCollection</a></code>,
  <code><a href="#htmlformcontrolscollection">HTMLFormControlsCollection</a></code>,
  <code><a href="#htmloptionscollection">HTMLOptionsCollection</a></code>,
  interfaces represent various
  lists of DOM nodes. Collectively, objects implementing these
  interfaces are called <dfn id="collections">collections</dfn>.</p><p>When a <a href="#collections" title="collections">collection</a> is created, a
  filter and a root are associated with the collection.</p><p class="example">For example, when the <code><a href="#htmlcollection">HTMLCollection</a></code>
  object for the <code title="dom-document-images"><a href="dom.html#dom-document-images">document.images</a></code> attribute is
  created, it is associated with a filter that selects only
  <code><a href="embedded-content-1.html#the-img-element">img</a></code> elements, and rooted at the root of the
  document.</p><p>The <a href="#collections" title="collections">collection</a> then <dfn id="represented-by-the-collection" title="represented by the collection">represents</dfn> a
  <a href="infrastructure.html#live">live</a> view of the subtree rooted at the collection's
  root, containing only nodes that match the given filter. The view is
  linear. <span class="impl">In the absence of specific requirements
  to the contrary, the nodes within the collection must be sorted in
  <a href="infrastructure.html#tree-order">tree order</a>.</span></p><div class="impl">

  <p class="note">The <code title="dom-table-rows"><a href="tabular-data.html#dom-table-rows">rows</a></code> list is
  not in tree order.</p>

  <p>An attribute that returns a collection must return the same
  object every time it is retrieved.</p>

  </div><h5 id="htmlcollection-0"><span class="secno">2.8.2.1 </span>HTMLCollection</h5><p>The <code><a href="#htmlcollection">HTMLCollection</a></code> interface represents a generic
  <a href="#collections" title="collections">collection</a> of elements.</p><pre class="idl">interface <dfn id="htmlcollection">HTMLCollection</dfn> {
  readonly attribute unsigned long <a href="#dom-htmlcollection-length" title="dom-HTMLCollection-length">length</a>;
  caller getter <a href="infrastructure.html#element">Element</a> <a href="#dom-htmlcollection-item" title="dom-HTMLCollection-item">item</a>(in unsigned long index);
  caller getter object <a href="#dom-htmlcollection-nameditem" title="dom-HTMLCollection-namedItem">namedItem</a>(in DOMString name); // only returns Element
};</pre><dl class="domintro"><dt><var title="">collection</var> . <code title="dom-HTMLCollection-length"><a href="#dom-htmlcollection-length">length</a></code></dt>
   <dd>
    <p>Returns the number of elements in the collection.</p>
   </dd>

   <dt><var title="">element</var> = <var title="">collection</var> . <code title="dom-HTMLCollection-item"><a href="#dom-htmlcollection-item">item</a></code>(<var title="">index</var>)</dt>
   <dt><var title="">collection</var>[<var title="">index</var>]</dt>
   <dt><var title="">collection</var>(<var title="">index</var>)</dt>
   <dd>
    <p>Returns the item with index <var title="">index</var> from the collection. The items are sorted in <a href="infrastructure.html#tree-order">tree order</a>.</p>
    <p>Returns null if <var title="">index</var> is out of range.</p>
   </dd>

   <dt><var title="">element</var> = <var title="">collection</var> . <code title="dom-HTMLCollection-namedItem"><a href="#dom-htmlcollection-nameditem">namedItem</a></code>(<var title="">name</var>)</dt>
   <dt><var title="">collection</var>[<var title="">name</var>]</dt>
   <dt><var title="">collection</var>(<var title="">name</var>)</dt>
   <dd>
    <p>Returns the first item with <a href="elements.html#concept-id" title="concept-id">ID</a> or name <var title="">name</var>
    from the collection.</p>
    <p>Returns null if no element with that <a href="elements.html#concept-id" title="concept-id">ID</a> or name could be found.</p>
    <p>Only <code><a href="text-level-semantics.html#the-a-element">a</a></code>, <code><a href="obsolete.html#the-applet-element">applet</a></code>, <code><a href="the-map-element.html#the-area-element">area</a></code>,
    <code><a href="the-iframe-element.html#the-embed-element">embed</a></code>, <code><a href="forms.html#the-form-element">form</a></code>, <code><a href="obsolete.html#frame">frame</a></code>,
    <code><a href="obsolete.html#frameset">frameset</a></code>, <code><a href="the-iframe-element.html#the-iframe-element">iframe</a></code>, <code><a href="embedded-content-1.html#the-img-element">img</a></code>, and
    <code><a href="the-iframe-element.html#the-object-element">object</a></code> elements can have a name for the purpose of
    this method; their name is given by the value of their <code title="">name</code> attribute.</p>
   </dd>
  </dl><div class="impl">

  <p>The object's <a href="infrastructure.html#supported-property-indices">supported property indices</a> are the
  numbers in the range zero to one less than the number of nodes
  <a href="#represented-by-the-collection">represented by the collection</a>. If there are no such
  elements, then there are no <a href="infrastructure.html#supported-property-indices">supported property
  indices</a>.</p>

  <p>The <dfn id="dom-htmlcollection-length" title="dom-HTMLCollection-length"><code>length</code></dfn>
  attribute must return the number of nodes <a href="#represented-by-the-collection">represented by the
  collection</a>.</p>

  <p>The <dfn id="dom-htmlcollection-item" title="dom-HTMLCollection-item"><code>item(<var title="">index</var>)</code></dfn> method must return the <var title="">index</var>th node in the collection. If there is no <var title="">index</var>th node in the collection, then the method must
  return null.</p>

  <p>The <a href="infrastructure.html#supported-property-names">supported property names</a> consist
  of the values of the <code title="">name</code> attributes of each
  <code><a href="text-level-semantics.html#the-a-element">a</a></code>, <code><a href="obsolete.html#the-applet-element">applet</a></code>, <code><a href="the-map-element.html#the-area-element">area</a></code>,
  <code><a href="the-iframe-element.html#the-embed-element">embed</a></code>, <code><a href="forms.html#the-form-element">form</a></code>, <code><a href="obsolete.html#frame">frame</a></code>,
  <code><a href="obsolete.html#frameset">frameset</a></code>, <code><a href="the-iframe-element.html#the-iframe-element">iframe</a></code>, <code><a href="embedded-content-1.html#the-img-element">img</a></code>, and
  <code><a href="the-iframe-element.html#the-object-element">object</a></code> element <a href="#represented-by-the-collection">represented by the
  collection</a> with a <code title="">name</code> attribute, plus
  the list of IDs that the elements <a href="#represented-by-the-collection">represented by the
  collection</a> have.</p>

  <p>The <dfn id="dom-htmlcollection-nameditem" title="dom-HTMLCollection-namedItem"><code>namedItem(<var title="">key</var>)</code></dfn> method must return the first node
  in the collection that matches either of the following
  requirements:</p>

  <ul><li>It is an <code><a href="text-level-semantics.html#the-a-element">a</a></code>, <code><a href="obsolete.html#the-applet-element">applet</a></code>,
   <code><a href="the-map-element.html#the-area-element">area</a></code>, <code><a href="the-iframe-element.html#the-embed-element">embed</a></code>, <code><a href="forms.html#the-form-element">form</a></code>,
   <code><a href="obsolete.html#frame">frame</a></code>, <code><a href="obsolete.html#frameset">frameset</a></code>, <code><a href="the-iframe-element.html#the-iframe-element">iframe</a></code>,
   <code><a href="embedded-content-1.html#the-img-element">img</a></code>, or <code><a href="the-iframe-element.html#the-object-element">object</a></code> element with a <code title="">name</code> attribute equal to <var title="">key</var>,
   or,</li>

   <li>It is an element with an <a href="elements.html#concept-id" title="concept-id">ID</a>
   equal to <var title="">key</var>.</li>

  </ul><p>If no such elements are found, then the method must return
  null.</p>

  </div><h5 id="htmlallcollection-0"><span class="secno">2.8.2.2 </span>HTMLAllCollection</h5><p>The <code><a href="#htmlallcollection">HTMLAllCollection</a></code> interface represents a generic
  <a href="#collections" title="collections">collection</a> of elements just like
  <code><a href="#htmlcollection">HTMLCollection</a></code>, with the exception that its <code title="dom-HTMLAllCollection-namedItem"><a href="#dom-htmlallcollection-nameditem">namedItem()</a></code> method
  returns an <code><a href="#htmlallcollection">HTMLAllCollection</a></code> object when there are
  multiple matching elements.</p><pre class="idl">interface <dfn id="htmlallcollection">HTMLAllCollection</dfn> : <a href="#htmlcollection">HTMLCollection</a> {
  // inherits <a href="#dom-htmlcollection-length" title="dom-HTMLCollection-length">length</a> and <a href="#dom-htmlcollection-item" title="dom-HTMLCollection-item">item</a>()
  caller getter object <a href="#dom-htmlallcollection-nameditem" title="dom-HTMLAllCollection-namedItem">namedItem</a>(in DOMString name); // overrides inherited namedItem()
  <a href="#htmlallcollection">HTMLAllCollection</a> <a href="#dom-htmlallcollection-tags" title="dom-HTMLAllCollection-tags">tags</a>(in DOMString tagName);
};</pre><dl class="domintro"><dt><var title="">collection</var> . <code title="dom-HTMLCollection-length"><a href="#dom-htmlcollection-length">length</a></code></dt>
   <dd>
    <p>Returns the number of elements in the collection.</p>
   </dd>

   <dt><var title="">element</var> = <var title="">collection</var> . <code title="dom-HTMLCollection-item"><a href="#dom-htmlcollection-item">item</a></code>(<var title="">index</var>)</dt>
   <dt><var title="">collection</var>[<var title="">index</var>]</dt>
   <dt><var title="">collection</var>(<var title="">index</var>)</dt>
   <dd>
    <p>Returns the item with index <var title="">index</var> from the collection. The items are sorted in <a href="infrastructure.html#tree-order">tree order</a>.</p>
    <p>Returns null if <var title="">index</var> is out of range.</p>
   </dd>

   <dt><var title="">element</var> = <var title="">collection</var> . <code title="dom-HTMLAllCollection-namedItem"><a href="#dom-htmlallcollection-nameditem">namedItem</a></code>(<var title="">name</var>)</dt>
   <dt><var title="">collection</var> = <var title="">collection</var> . <code title="dom-HTMLAllCollection-namedItem"><a href="#dom-htmlallcollection-nameditem">namedItem</a></code>(<var title="">name</var>)</dt>
   <dt><var title="">collection</var>[<var title="">name</var>]</dt>
   <dt><var title="">collection</var>(<var title="">name</var>)</dt>
   <dd>
    <p>Returns the item with <a href="elements.html#concept-id" title="concept-id">ID</a> or name <var title="">name</var> from the collection.</p>
    <p>If there are multiple matching items, then an <code><a href="#htmlallcollection">HTMLAllCollection</a></code> object containing all those elements is returned.</p>
    <p>Returns null if no element with that <a href="elements.html#concept-id" title="concept-id">ID</a> or name could be found.</p>
    <p>Only <code><a href="text-level-semantics.html#the-a-element">a</a></code>, <code><a href="obsolete.html#the-applet-element">applet</a></code>, <code><a href="the-map-element.html#the-area-element">area</a></code>,
    <code><a href="the-iframe-element.html#the-embed-element">embed</a></code>, <code><a href="forms.html#the-form-element">form</a></code>, <code><a href="obsolete.html#frame">frame</a></code>,
    <code><a href="obsolete.html#frameset">frameset</a></code>, <code><a href="the-iframe-element.html#the-iframe-element">iframe</a></code>, <code><a href="embedded-content-1.html#the-img-element">img</a></code>, and
    <code><a href="the-iframe-element.html#the-object-element">object</a></code> elements can have a name for the purpose of
    this method; their name is given by the value of their <code title="">name</code> attribute.</p>
   </dd>

   <dt><var title="">collection</var> = <var title="">collection</var> . <code title="dom-HTMLAllCollection-tags"><a href="#dom-htmlallcollection-tags">tags</a></code>(<var title="">tagName</var>)</dt>
   <dd>
    <p>Returns a collection that is a filtered view of the current collection, containing only elements with the given tag name.</p>
   </dd>

  </dl><div class="impl">

  <p>The object's <a href="infrastructure.html#supported-property-indices">supported property indices</a> and
  <a href="infrastructure.html#supported-property-names">supported property names</a> are as defined for
  <code><a href="#htmlcollection">HTMLCollection</a></code> objects.</p>

  <p>The <dfn id="dom-htmlallcollection-nameditem" title="dom-HTMLAllCollection-namedItem"><code>namedItem(<var title="">key</var>)</code></dfn> method must act according to the
  following algorithm:</p>

  <ol><li>

    <p>Let <var title="">collection</var> be an
    <code><a href="#htmlallcollection">HTMLAllCollection</a></code> object rooted at the same node as
    the <code><a href="#htmlallcollection">HTMLAllCollection</a></code> object on which the method was
    invoked, whose filter matches only elements that already
    match the filter of the <code><a href="#htmlallcollection">HTMLAllCollection</a></code> object on
    which the method was invoked and that are either:</p>

    <ul><li><code><a href="text-level-semantics.html#the-a-element">a</a></code>, <code><a href="obsolete.html#the-applet-element">applet</a></code>, <code><a href="the-map-element.html#the-area-element">area</a></code>,
     <code><a href="the-iframe-element.html#the-embed-element">embed</a></code>, <code><a href="forms.html#the-form-element">form</a></code>, <code><a href="obsolete.html#frame">frame</a></code>,
     <code><a href="obsolete.html#frameset">frameset</a></code>, <code><a href="the-iframe-element.html#the-iframe-element">iframe</a></code>, <code><a href="embedded-content-1.html#the-img-element">img</a></code>, or
     <code><a href="the-iframe-element.html#the-object-element">object</a></code> elements with a <code title="">name</code>
     attribute equal to <var title="">key</var>, or,</li>

     <li>elements with an <a href="elements.html#concept-id" title="concept-id">ID</a> equal to
     <var title="">key</var>.</li>

    </ul></li>

   <li>If, at the time the method is called, there is exactly one node
   in <var title="">collection</var>, then return that node and stop
   the algorithm.</li>

   <li>Otherwise, if, at the time the method is called, <var title="">collection</var> is empty, return null and stop the
   algorithm.</li>

   <li>Otherwise, return <var title="">collection</var>.</li>

  </ol><p>The <dfn id="dom-htmlallcollection-tags" title="dom-HTMLAllCollection-tags"><code>tags(<var title="">tagName</var>)</code></dfn> method must return an
  <code><a href="#htmlallcollection">HTMLAllCollection</a></code> rooted at the same node as the
  <code><a href="#htmlallcollection">HTMLAllCollection</a></code> object on which the method was
  invoked, whose filter matches only <a href="infrastructure.html#html-elements">HTML elements</a> whose
  local name is the <var title="">tagName</var> argument and that
  already match the filter of the <code><a href="#htmlallcollection">HTMLAllCollection</a></code>
  object on which the method was invoked. In <a href="dom.html#html-documents">HTML
  documents</a>, the argument must first be <a href="infrastructure.html#converted-to-ascii-lowercase">converted to
  ASCII lowercase</a>.</p>

  </div><h5 id="htmlformcontrolscollection-0"><span class="secno">2.8.2.3 </span>HTMLFormControlsCollection</h5><p>The <code><a href="#htmlformcontrolscollection">HTMLFormControlsCollection</a></code> interface represents
  a <a href="#collections" title="collections">collection</a> of <a href="forms.html#category-listed" title="category-listed">listed elements</a> in <code><a href="forms.html#the-form-element">form</a></code>
  and <code><a href="forms.html#the-fieldset-element">fieldset</a></code> elements.</p><pre class="idl">interface <dfn id="htmlformcontrolscollection">HTMLFormControlsCollection</dfn> : <a href="#htmlcollection">HTMLCollection</a> {
  // inherits <a href="#dom-htmlcollection-length" title="dom-HTMLCollection-length">length</a> and <a href="#dom-htmlcollection-item" title="dom-HTMLCollection-item">item</a>()
  caller getter object <a href="#dom-htmlformcontrolscollection-nameditem" title="dom-HTMLFormControlsCollection-namedItem">namedItem</a>(in DOMString name); // overrides inherited namedItem()
};

interface <dfn id="radionodelist">RadioNodeList</dfn> : <a href="infrastructure.html#nodelist">NodeList</a> {
          attribute DOMString <a href="#dom-radionodelist-value" title="dom-RadioNodeList-value">value</a>;
};</pre><dl class="domintro"><dt><var title="">collection</var> . <code title="dom-HTMLCollection-length"><a href="#dom-htmlcollection-length">length</a></code></dt>
   <dd>
    <p>Returns the number of elements in the collection.</p>
   </dd>

   <dt><var title="">element</var> = <var title="">collection</var> . <code title="dom-HTMLCollection-item"><a href="#dom-htmlcollection-item">item</a></code>(<var title="">index</var>)</dt>
   <dt><var title="">collection</var>[<var title="">index</var>]</dt>
   <dt><var title="">collection</var>(<var title="">index</var>)</dt>
   <dd>
    <p>Returns the item with index <var title="">index</var> from the collection. The items are sorted in <a href="infrastructure.html#tree-order">tree order</a>.</p>
    <p>Returns null if <var title="">index</var> is out of range.</p>
   </dd>

   <dt><var title="">element</var> = <var title="">collection</var> . <code title="dom-HTMLFormControlsCollection-namedItem"><a href="#dom-htmlformcontrolscollection-nameditem">namedItem</a></code>(<var title="">name</var>)</dt>
   <dt><var title="">radioNodeList</var> = <var title="">collection</var> . <code title="dom-HTMLFormControlsCollection-namedItem"><a href="#dom-htmlformcontrolscollection-nameditem">namedItem</a></code>(<var title="">name</var>)</dt>
   <dt><var title="">collection</var>[<var title="">name</var>]</dt>
   <dt><var title="">collection</var>(<var title="">name</var>)</dt>
   <dd>
    <p>Returns the item with <a href="elements.html#concept-id" title="concept-id">ID</a> or <code title="attr-fe-name"><a href="association-of-controls-and-forms.html#attr-fe-name">name</a></code> <var title="">name</var> from the collection.</p>
    <p>If there are multiple matching items, then a <code><a href="#radionodelist">RadioNodeList</a></code> object containing all those elements is returned.</p>
    <p>Returns null if no element with that <a href="elements.html#concept-id" title="concept-id">ID</a> or <code title="attr-fe-name"><a href="association-of-controls-and-forms.html#attr-fe-name">name</a></code> could be found.</p>
   </dd>

   <dt><var title="">radioNodeList</var> . <var title="">value</var> [ = <var title="">value</var> ]</dt>
   <dd>
    <p>Returns the value of the first checked radio button represented by the object.</p>
    <p>Can be set, to check the first radio button with the given value represented by the object.</p>
   </dd>

  </dl><div class="impl">

  <p>The object's <a href="infrastructure.html#supported-property-indices">supported property indices</a> are as
  defined for <code><a href="#htmlcollection">HTMLCollection</a></code> objects.</p>

  <p>The <a href="infrastructure.html#supported-property-names">supported property names</a> consist of the values
  of all the <code title="attr-id"><a href="elements.html#the-id-attribute">id</a></code> and <code title="attr-fe-name"><a href="association-of-controls-and-forms.html#attr-fe-name">name</a></code> attributes of all the elements
  <a href="#represented-by-the-collection">represented by the collection</a>.</p>

  <p>The <dfn id="dom-htmlformcontrolscollection-nameditem" title="dom-HTMLFormControlsCollection-namedItem"><code>namedItem(<var title="">name</var>)</code></dfn> method must act according to the
  following algorithm:</p>

  <ol><li>If, at the time the method is called, there is exactly one node
   in the collection that has either an <code title="attr-id"><a href="elements.html#the-id-attribute">id</a></code> attribute or a <code title="attr-fe-name"><a href="association-of-controls-and-forms.html#attr-fe-name">name</a></code> attribute equal to <var title="">name</var>, then return that node and stop the
   algorithm.</li>

   <li>Otherwise, if there are no nodes in the collection that have
   either an <code title="attr-id"><a href="elements.html#the-id-attribute">id</a></code> attribute or a <code title="attr-fe-name"><a href="association-of-controls-and-forms.html#attr-fe-name">name</a></code> attribute equal to <var title="">name</var>, then return null and stop the algorithm.</li>

   <li>Otherwise, create a new <code><a href="#radionodelist">RadioNodeList</a></code> object
   representing a <a href="infrastructure.html#live">live</a> view of the
   <code><a href="#htmlformcontrolscollection">HTMLFormControlsCollection</a></code> object, further filtered so
   that the only nodes in the <code><a href="#radionodelist">RadioNodeList</a></code> object are
   those that have either an <code title="attr-id"><a href="elements.html#the-id-attribute">id</a></code> attribute
   or a <code title="attr-fe-name"><a href="association-of-controls-and-forms.html#attr-fe-name">name</a></code> attribute equal to <var title="">name</var>. The nodes in the <code><a href="#radionodelist">RadioNodeList</a></code>
   object must be sorted in <a href="infrastructure.html#tree-order">tree order</a>.</li>

   <li>Return that <code><a href="#radionodelist">RadioNodeList</a></code> object.</li>

  </ol><hr><p>Members of the <code><a href="#radionodelist">RadioNodeList</a></code> interface inherited
  from the <code><a href="infrastructure.html#nodelist">NodeList</a></code> interface must behave as they would
  on a <code><a href="infrastructure.html#nodelist">NodeList</a></code> object.</p>

  <p>The <dfn id="dom-radionodelist-value" title="dom-RadioNodeList-value"><code>value</code></dfn>
  IDL attribute on the <code><a href="#radionodelist">RadioNodeList</a></code> object, on getting,
  must return the value returned by running the following steps:</p>

  <ol><li><p>Let <var title="">element</var> be the first element in
   <a href="infrastructure.html#tree-order">tree order</a> represented by the
   <code><a href="#radionodelist">RadioNodeList</a></code> object that is an <code><a href="the-input-element.html#the-input-element">input</a></code>
   element whose <code title="attr-input-type"><a href="the-input-element.html#attr-input-type">type</a></code> attribute
   is in the <a href="number-state.html#radio-button-state" title="attr-input-type-radio">Radio Button</a>
   state and whose <a href="association-of-controls-and-forms.html#concept-fe-checked" title="concept-fe-checked">checkedness</a>
   is true. Otherwise, let it be null.</p></li>

   <li><p>If <var title="">element</var> is null, or if it is an
   element with no <code title="attr-input-value"><a href="the-input-element.html#attr-input-value">value</a></code>
   attribute, return the empty string.</p></li>

   <li><p>Otherwise, return the value of <var title="">element</var>'s
   <code title="attr-input-value"><a href="the-input-element.html#attr-input-value">value</a></code> attribute.</p></li>

  </ol><p>On setting, the <code title="dom-RadioNodeList-value"><a href="#dom-radionodelist-value">value</a></code> IDL attribute must run
  the following steps:</p>

  <ol><li><p>Let <var title="">element</var> be the first element in
   <a href="infrastructure.html#tree-order">tree order</a> represented by the
   <code><a href="#radionodelist">RadioNodeList</a></code> object that is an <code><a href="the-input-element.html#the-input-element">input</a></code>
   element whose <code title="attr-input-type"><a href="the-input-element.html#attr-input-type">type</a></code> attribute
   is in the <a href="number-state.html#radio-button-state" title="attr-input-type-radio">Radio Button</a>
   state and whose <code title="attr-input-value"><a href="the-input-element.html#attr-input-value">value</a></code> content
   attribute is present and equal to the new value, if any. Otherwise,
   let it be null.</p></li>

   <li><p>If <var title="">element</var> is not null, then set its
   <a href="association-of-controls-and-forms.html#concept-fe-checked" title="concept-fe-checked">checkedness</a> to true.</p>

  </li></ol></div><h5 id="htmloptionscollection-0"><span class="secno">2.8.2.4 </span>HTMLOptionsCollection</h5><p>The <code><a href="#htmloptionscollection">HTMLOptionsCollection</a></code> interface represents a
  list of <code><a href="the-button-element.html#the-option-element">option</a></code> elements. It is always rooted on a
  <code><a href="the-button-element.html#the-select-element">select</a></code> element and has attributes and methods that
  manipulate that element's descendants.</p><pre class="idl">interface <dfn id="htmloptionscollection">HTMLOptionsCollection</dfn> : <a href="#htmlcollection">HTMLCollection</a> {
  // inherits <a href="#dom-htmlcollection-item" title="dom-HTMLCollection-item">item</a>()
           attribute unsigned long <a href="#dom-htmloptionscollection-length" title="dom-HTMLOptionsCollection-length">length</a>; // overrides inherited length
  caller getter object <a href="#dom-htmloptionscollection-nameditem" title="dom-HTMLOptionsCollection-namedItem">namedItem</a>(in DOMString name); // overrides inherited namedItem()
  void <a href="#dom-htmloptionscollection-add" title="dom-HTMLOptionsCollection-add">add</a>(in <a href="elements.html#htmlelement">HTMLElement</a> element, in optional <a href="elements.html#htmlelement">HTMLElement</a> before);
  void <a href="#dom-htmloptionscollection-add" title="dom-HTMLOptionsCollection-add">add</a>(in <a href="elements.html#htmlelement">HTMLElement</a> element, in long before);
  void <a href="#dom-htmloptionscollection-remove" title="dom-HTMLOptionsCollection-remove">remove</a>(in long index);
           attribute long <a href="#dom-htmloptionscollection-selectedindex" title="dom-HTMLOptionsCollection-selectedIndex">selectedIndex</a>;
};</pre><dl class="domintro"><dt><var title="">collection</var> . <code title="dom-HTMLOptionsCollection-length"><a href="#dom-htmloptionscollection-length">length</a></code> [ = <var title="">value</var> ]</dt>
   <dd>
    <p>Returns the number of elements in the collection.</p>
    <p>When set to a smaller number, truncates the number of <code><a href="the-button-element.html#the-option-element">option</a></code> elements in the corresponding container.</p>
    <p>When set to a greater number, adds new blank <code><a href="the-button-element.html#the-option-element">option</a></code> elements to that container.</p>
   </dd>

   <dt><var title="">element</var> = <var title="">collection</var> . <code title="dom-HTMLCollection-item"><a href="#dom-htmlcollection-item">item</a></code>(<var title="">index</var>)</dt>
   <dt><var title="">collection</var>[<var title="">index</var>]</dt>
   <dt><var title="">collection</var>(<var title="">index</var>)</dt>
   <dd>
    <p>Returns the item with index <var title="">index</var> from the collection. The items are sorted in <a href="infrastructure.html#tree-order">tree order</a>.</p>
    <p>Returns null if <var title="">index</var> is out of range.</p>
   </dd>

   <dt><var title="">element</var> = <var title="">collection</var> . <code title="dom-HTMLOptionsCollection-namedItem"><a href="#dom-htmloptionscollection-nameditem">namedItem</a></code>(<var title="">name</var>)</dt>
   <dt><var title="">nodeList</var> = <var title="">collection</var> . <code title="dom-HTMLOptionsCollection-namedItem"><a href="#dom-htmloptionscollection-nameditem">namedItem</a></code>(<var title="">name</var>)</dt>
   <dt><var title="">collection</var>[<var title="">name</var>]</dt>
   <dt><var title="">collection</var>(<var title="">name</var>)</dt>
   <dd>
    <p>Returns the item with <a href="elements.html#concept-id" title="concept-id">ID</a> or <code title="attr-option-name"><a href="obsolete.html#attr-option-name">name</a></code> <var title="">name</var> from the collection.</p>
    <p>If there are multiple matching items, then a <code><a href="infrastructure.html#nodelist">NodeList</a></code> object containing all those elements is returned.</p>
    <p>Returns null if no element with that <a href="elements.html#concept-id" title="concept-id">ID</a> could be found.</p>
   </dd>

   <dt><var title="">collection</var> . <code title="dom-HTMLOptionsCollection-add"><a href="#dom-htmloptionscollection-add">add</a></code>(<var title="">element</var> [, <var title="">before</var> ] )</dt>
   <dd>
    <p>Inserts <var title="">element</var> before the node given by <var title="">before</var>.</p>
    <p>The <var title="">before</var> argument can be a number, in
    which case <var title="">element</var> is inserted before the item
    with that number, or an element from the collection, in which case
    <var title="">element</var> is inserted before that element.</p>
    <p>If <var title="">before</var> is omitted, null, or a number out
    of range, then <var title="">element</var> will be added at the
    end of the list.</p>
    <p>This method will throw a <code><a href="#hierarchy_request_err">HIERARCHY_REQUEST_ERR</a></code>
    exception if <var title="">element</var> is an ancestor of the
    element into which it is to be inserted. If <var title="">element</var> is not an <code><a href="the-button-element.html#the-option-element">option</a></code> or
    <code><a href="the-button-element.html#the-optgroup-element">optgroup</a></code> element, then the method does nothing.</p>
   </dd>

   <dt><var title="">collection</var> . <code title="dom-HTMLOptionsCollection-selectedIndex"><a href="#dom-htmloptionscollection-selectedindex">selectedIndex</a></code> [ = <var title="">value</var> ]</dt>

   <dd>

    <p>Returns the index of the first selected item, if any, or
    &#8722;1 if there is no selected item.</p>

    <p>Can be set, to change the selection.</p>

   </dd>

  </dl><div class="impl">

  <p>The object's <a href="infrastructure.html#supported-property-indices">supported property indices</a> are as
  defined for <code><a href="#htmlcollection">HTMLCollection</a></code> objects.</p>

  <p>On getting, the <dfn id="dom-htmloptionscollection-length" title="dom-HTMLOptionsCollection-length"><code>length</code></dfn>
  attribute must return the number of nodes <a href="#represented-by-the-collection">represented by the
  collection</a>.</p>

  <p>On setting, the behavior depends on whether the new value is
  equal to, greater than, or less than the number of nodes
  <a href="#represented-by-the-collection">represented by the collection</a> at that time. If the
  number is the same, then setting the attribute must do nothing. If
  the new value is greater, then <var title="">n</var> new
  <code><a href="the-button-element.html#the-option-element">option</a></code> elements with no attributes and no child nodes
  must be appended to the <code><a href="the-button-element.html#the-select-element">select</a></code> element on which the
  <code><a href="#htmloptionscollection">HTMLOptionsCollection</a></code> is rooted, where <var title="">n</var> is the difference between the two numbers (new
  value minus old value). Mutation events must be fired as if a
  <code><a href="infrastructure.html#documentfragment">DocumentFragment</a></code> containing the new <code><a href="the-button-element.html#the-option-element">option</a></code>
  elements had been inserted.  If the new value is lower, then the
  last <var title="">n</var> nodes in the collection must be removed
  from their parent nodes, where <var title="">n</var> is the
  difference between the two numbers (old value minus new value).</p>

  <p class="note">Setting <code title="dom-HTMLOptionsCollection-length"><a href="#dom-htmloptionscollection-length">length</a></code> never removes
  or adds any <code><a href="the-button-element.html#the-optgroup-element">optgroup</a></code> elements, and never adds new
  children to existing <code><a href="the-button-element.html#the-optgroup-element">optgroup</a></code> elements (though it can
  remove children from them).</p>

  <p>The <a href="infrastructure.html#supported-property-names">supported property names</a> consist of the values
  of all the <code title="attr-id"><a href="elements.html#the-id-attribute">id</a></code> and <code title="attr-option-name"><a href="obsolete.html#attr-option-name">name</a></code> attributes of all the elements
  <a href="#represented-by-the-collection">represented by the collection</a>.</p>

  <p>The <dfn id="dom-htmloptionscollection-nameditem" title="dom-HTMLOptionsCollection-namedItem"><code>namedItem(<var title="">name</var>)</code></dfn> method must act according to the
  following algorithm:</p>

  <ol><li>If, at the time the method is called, there is exactly one node
   in the collection that has either an <code title="attr-id"><a href="elements.html#the-id-attribute">id</a></code> attribute or a <code title="attr-option-name"><a href="obsolete.html#attr-option-name">name</a></code> attribute equal to <var title="">name</var>, then return that node and stop the
   algorithm.</li>

   <li>Otherwise, if there are no nodes in the collection that have
   either an <code title="attr-id"><a href="elements.html#the-id-attribute">id</a></code> attribute or a <code title="attr-option-name"><a href="obsolete.html#attr-option-name">name</a></code> attribute equal to <var title="">name</var>, then return null and stop the algorithm.</li>

   
   <li>Otherwise, create a new <code><a href="infrastructure.html#nodelist">NodeList</a></code> object
   representing a <a href="infrastructure.html#live">live</a> view of the
   <code><a href="#htmloptionscollection">HTMLOptionsCollection</a></code> object, further filtered so that
   the only nodes in the <code><a href="infrastructure.html#nodelist">NodeList</a></code> object are those that
   have either an <code title="attr-id"><a href="elements.html#the-id-attribute">id</a></code> attribute or a <code title="attr-option-name"><a href="obsolete.html#attr-option-name">name</a></code> attribute equal to <var title="">name</var>. The nodes in the <code><a href="infrastructure.html#nodelist">NodeList</a></code> object
   must be sorted in <a href="infrastructure.html#tree-order">tree order</a>.</li>

   <li>Return that <code><a href="infrastructure.html#nodelist">NodeList</a></code> object.</li>

  </ol><p>The <dfn id="dom-htmloptionscollection-add" title="dom-HTMLOptionsCollection-add"><code>add(<var title="">element</var>, <var title="">before</var>)</code></dfn>
  method must act according to the following algorithm:</p>

  <ol><li><p>If <var title="">element</var> is not an <code><a href="the-button-element.html#the-option-element">option</a></code>
   or <code><a href="the-button-element.html#the-optgroup-element">optgroup</a></code> element, then return and abort these
   steps.</p></li>

   <li><p>If <var title="">element</var> is an ancestor of the
   <code><a href="the-button-element.html#the-select-element">select</a></code> element on which the
   <code><a href="#htmloptionscollection">HTMLOptionsCollection</a></code> is rooted, then throw a
   <code><a href="#hierarchy_request_err">HIERARCHY_REQUEST_ERR</a></code> exception.</p></li>

   <li><p>If <var title="">before</var> is an element, but that
   element isn't a descendant of the <code><a href="the-button-element.html#the-select-element">select</a></code> element on
   which the <code><a href="#htmloptionscollection">HTMLOptionsCollection</a></code> is rooted, then throw
   a <code><a href="#not_found_err">NOT_FOUND_ERR</a></code> exception.</p></li>

   <li><p>If <var title="">element</var> and <var title="">before</var> are the same element, then return and abort
   these steps.</p></li>

   <li><p>If <var title="">before</var> is a node, then let <var title="">reference</var> be that node. Otherwise, if <var title="">before</var> is an integer, and there is a <var title="">before</var>th node in the collection, let <var title="">reference</var> be that node. Otherwise, let <var title="">reference</var> be null.</p></li>

   <li><p>If <var title="">reference</var> is not null, let <var title="">parent</var> be the parent node of <var title="">reference</var>. Otherwise, let <var title="">parent</var>
   be the <code><a href="the-button-element.html#the-select-element">select</a></code> element on which the
   <code><a href="#htmloptionscollection">HTMLOptionsCollection</a></code> is rooted.</p></li>

   <li><p>Act as if the DOM Core <code title="dom-Node-insertBefore"><a href="infrastructure.html#dom-node-insertbefore">insertBefore()</a></code> method was
   invoked on the <var title="">parent</var> node, with <var title="">element</var> as the first argument and <var title="">reference</var> as the second argument.</p>

  </li></ol><p>The <dfn id="dom-htmloptionscollection-remove" title="dom-HTMLOptionsCollection-remove"><code>remove(<var title="">index</var>)</code></dfn> method must act according to
  the following algorithm:</p>

  <ol><li><p>If the number of nodes <a href="#represented-by-the-collection">represented by the
   collection</a> is zero, abort these steps.</p></li>

   <li><p>If <var title="">index</var> is not a number greater than or
   equal to 0 and less than the number of nodes <a href="#represented-by-the-collection">represented by
   the collection</a>, let <var title="">element</var> be the first
   element in the collection. Otherwise, let <var title="">element</var> be the <var title="">index</var>th element
   in the collection.</p></li>

   <li><p>Remove <var title="">element</var> from its parent
   node.</p></li>

  </ol><p>The <dfn id="dom-htmloptionscollection-selectedindex" title="dom-HTMLOptionsCollection-selectedIndex"><code>selectedIndex</code></dfn>
  IDL attribute must act like the identically named attribute on the
  <code><a href="the-button-element.html#the-select-element">select</a></code> element on which the
  <code><a href="#htmloptionscollection">HTMLOptionsCollection</a></code> is rooted</p>

  

  </div><h4 id="domtokenlist-0"><span class="secno">2.8.3 </span>DOMTokenList</h4><p>The <code><a href="#domtokenlist">DOMTokenList</a></code> interface represents an interface
  to an underlying string that consists of a <a href="common-microsyntaxes.html#set-of-space-separated-tokens">set of
  space-separated tokens</a>.</p><p class="note"><code><a href="#domtokenlist">DOMTokenList</a></code> objects are always
  <a href="infrastructure.html#case-sensitive">case-sensitive</a>, even when the underlying string might
  ordinarily be treated in a case-insensitive manner.</p><pre class="idl">interface <dfn id="domtokenlist">DOMTokenList</dfn> {
  readonly attribute unsigned long <a href="#dom-tokenlist-length" title="dom-tokenlist-length">length</a>;
  getter DOMString <a href="#dom-tokenlist-item" title="dom-tokenlist-item">item</a>(in unsigned long index);
  boolean <a href="#dom-tokenlist-contains" title="dom-tokenlist-contains">contains</a>(in DOMString token);
  void <a href="#dom-tokenlist-add" title="dom-tokenlist-add">add</a>(in DOMString token);
  void <a href="#dom-tokenlist-remove" title="dom-tokenlist-remove">remove</a>(in DOMString token);
  boolean <a href="#dom-tokenlist-toggle" title="dom-tokenlist-toggle">toggle</a>(in DOMString token);
  <a href="#dom-tokenlist-tostring" title="dom-tokenlist-toString">stringifier</a> DOMString ();
};</pre><dl class="domintro"><dt><var title="">tokenlist</var> . <code title="dom-tokenlist-length"><a href="#dom-tokenlist-length">length</a></code></dt>
   <dd>
    <p>Returns the number of tokens in the string.</p>
   </dd>

   <dt><var title="">element</var> = <var title="">tokenlist</var> . <code title="dom-tokenlist-item"><a href="#dom-tokenlist-item">item</a></code>(<var title="">index</var>)</dt>
   <dt><var title="">tokenlist</var>[<var title="">index</var>]</dt>
   <dd>
    <p>Returns the token with index <var title="">index</var>. The tokens are returned in the order they are found in the underlying string.</p>
    <p>Returns null if <var title="">index</var> is out of range.</p>
   </dd>

   <dt><var title="">hastoken</var> = <var title="">tokenlist</var> . <code title="dom-tokenlist-contains"><a href="#dom-tokenlist-contains">contains</a></code>(<var title="">token</var>)</dt>
   <dd>
    <p>Returns true if the <var title="">token</var> is present; false otherwise.</p>
    <p>Throws a <code><a href="#syntax_err">SYNTAX_ERR</a></code> exception if <var title="">token</var> is empty.</p>
    <p>Throws an <code><a href="#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception if <var title="">token</var> contains any spaces.</p>
   </dd>

   <dt><var title="">tokenlist</var> . <code title="dom-tokenlist-add"><a href="#dom-tokenlist-add">add</a></code>(<var title="">token</var>)</dt>
   <dd>
    <p>Adds <var title="">token</var>, unless it is already present.</p>
    <p>Throws a <code><a href="#syntax_err">SYNTAX_ERR</a></code> exception if <var title="">token</var> is empty.</p>
    <p>Throws an <code><a href="#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception if <var title="">token</var> contains any spaces.</p>
   </dd>

   <dt><var title="">tokenlist</var> . <code title="dom-tokenlist-remove"><a href="#dom-tokenlist-remove">remove</a></code>(<var title="">token</var>)</dt>
   <dd>
    <p>Removes <var title="">token</var> if it is present.</p>
    <p>Throws a <code><a href="#syntax_err">SYNTAX_ERR</a></code> exception if <var title="">token</var> is empty.</p>
    <p>Throws an <code><a href="#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception if <var title="">token</var> contains any spaces.</p>
   </dd>

   <dt><var title="">hastoken</var> = <var title="">tokenlist</var> . <code title="dom-tokenlist-toggle"><a href="#dom-tokenlist-toggle">toggle</a></code>(<var title="">token</var>)</dt>
   <dd>
    <p>Adds <var title="">token</var> if it is not present, or removes
    it if it is. Returns true if <var title="">token</var> is now
    present (it was added); returns false if it is not (it was
    removed).</p>
    <p>Throws a <code><a href="#syntax_err">SYNTAX_ERR</a></code> exception if <var title="">token</var> is empty.</p>
    <p>Throws an <code><a href="#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception if <var title="">token</var> contains any spaces.</p>
   </dd>

  </dl><div class="impl">

  <p>The <dfn id="dom-tokenlist-length" title="dom-tokenlist-length"><code>length</code></dfn>
  attribute must return the number of tokens that result from <a href="common-microsyntaxes.html#split-a-string-on-spaces" title="split a string on spaces">splitting the underlying string on
  spaces</a>. This is the <var title="dom-tokenlist-length"><a href="#dom-tokenlist-length">length</a></var>.</p>

  <p>The object's <a href="infrastructure.html#supported-property-indices">supported property indices</a> are the
  numbers in the range zero to <span title=""><var title="dom-tokenlist-length"><a href="#dom-tokenlist-length">length</a></var>-1</span>, unless the <var title="dom-tokenlist-length"><a href="#dom-tokenlist-length">length</a></var> is zero, in which case
  there are no <a href="infrastructure.html#supported-property-indices">supported property indices</a>.</p>

  <p>The <dfn id="dom-tokenlist-item" title="dom-tokenlist-item"><code>item(<var title="">index</var>)</code></dfn> method must <a href="common-microsyntaxes.html#split-a-string-on-spaces" title="split a
  string on spaces">split the underlying string on spaces</a>,
  preserving the order of the tokens as found in the underlying
  string, and then return the <var title="">index</var>th item in this
  list. If <var title="">index</var> is equal to or greater than the
  number of tokens, then the method must return null.</p>

  <p class="example">For example, if the string is "<code title="">a b
  a c</code>" then there are four tokens: the token with index 0 is
  "<code title="">a</code>", the token with index 1 is "<code title="">b</code>", the token with index 2 is "<code title="">a</code>", and the token with index 3 is "<code title="">c</code>".</p>

  <p>The <dfn id="dom-tokenlist-contains" title="dom-tokenlist-contains"><code>contains(<var title="">token</var>)</code></dfn> method must run the following
  algorithm:</p>

  <ol><li>If the <var title="">token</var> argument is the empty string,
   then raise a <code><a href="#syntax_err">SYNTAX_ERR</a></code> exception and stop the
   algorithm.</li>

   <li>If the <var title="">token</var> argument contains any <a href="common-microsyntaxes.html#space-character" title="space character">space characters</a>, then raise an
   <code><a href="#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception and stop the
   algorithm.</li>

   <li>Otherwise, <a href="common-microsyntaxes.html#split-a-string-on-spaces" title="split a string on spaces">split the
   underlying string on spaces</a> to get the list of tokens in the
   <code><a href="#domtokenlist">DOMTokenList</a></code> object's underlying string.</li>

   <li>If the token indicated by <var title="">token</var> is a
   <a href="infrastructure.html#case-sensitive">case-sensitive</a> match for one of the tokens in the
   <code><a href="#domtokenlist">DOMTokenList</a></code> object's underlying string then return
   true and stop this algorithm.</li>

   <li>Otherwise, return false.</li>

  </ol><p>The <dfn id="dom-tokenlist-add" title="dom-tokenlist-add"><code>add(<var title="">token</var>)</code></dfn> method must run the following
  algorithm:</p>

  <ol><li>If the <var title="">token</var> argument is the empty string,
   then raise a <code><a href="#syntax_err">SYNTAX_ERR</a></code> exception and stop the
   algorithm.</li>

   <li>If the <var title="">token</var> argument contains any <a href="common-microsyntaxes.html#space-character" title="space character">space characters</a>, then raise an
   <code><a href="#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception and stop the
   algorithm.</li>

   <li>Otherwise, <a href="common-microsyntaxes.html#split-a-string-on-spaces" title="split a string on spaces">split the
   underlying string on spaces</a> to get the list of tokens in the
   <code><a href="#domtokenlist">DOMTokenList</a></code> object's underlying string.</li>

   <li>If the given <var title="">token</var> is a
   <a href="infrastructure.html#case-sensitive">case-sensitive</a> match for one of the tokens in the
   <code><a href="#domtokenlist">DOMTokenList</a></code> object's underlying string then stop the
   algorithm.</li>

   <li>Otherwise, if the <code><a href="#domtokenlist">DOMTokenList</a></code> object's underlying
   string is not the empty string and the last character of that
   string is not a <a href="common-microsyntaxes.html#space-character">space character</a>, then append a U+0020
   SPACE character to the end of that string.</li>

   <li>Append the value of <var title="">token</var> to the end of the
   <code><a href="#domtokenlist">DOMTokenList</a></code> object's underlying string.</li>

  </ol><p>The <dfn id="dom-tokenlist-remove" title="dom-tokenlist-remove"><code>remove(<var title="">token</var>)</code></dfn> method must run the following
  algorithm:</p>

  <ol><li>If the <var title="">token</var> argument is the empty string,
   then raise a <code><a href="#syntax_err">SYNTAX_ERR</a></code> exception and stop the
   algorithm.</li>

   <li>If the <var title="">token</var> argument contains any <a href="common-microsyntaxes.html#space-character" title="space character">space characters</a>, then raise an
   <code><a href="#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception and stop the
   algorithm.</li>

   <li>Otherwise, <a href="common-microsyntaxes.html#remove-a-token-from-a-string" title="remove a token from a string">remove
   the given <var title="">token</var> from the underlying
   string</a>.</li>

  </ol><p>The <dfn id="dom-tokenlist-toggle" title="dom-tokenlist-toggle"><code>toggle(<var title="">token</var>)</code></dfn> method must run the following
  algorithm:</p>

  <ol><li>If the <var title="">token</var> argument is the empty string,
   then raise a <code><a href="#syntax_err">SYNTAX_ERR</a></code> exception and stop the
   algorithm.</li>

   <li>If the <var title="">token</var> argument contains any <a href="common-microsyntaxes.html#space-character" title="space character">space characters</a>, then raise an
   <code><a href="#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception and stop the
   algorithm.</li>

   <li>Otherwise, <a href="common-microsyntaxes.html#split-a-string-on-spaces" title="split a string on spaces">split the
   underlying string on spaces</a> to get the list of tokens in the
   <code><a href="#domtokenlist">DOMTokenList</a></code> object's underlying string.</li>

   <li>If the given <var title="">token</var> is a
   <a href="infrastructure.html#case-sensitive">case-sensitive</a> match for one of the tokens in the
   <code><a href="#domtokenlist">DOMTokenList</a></code> object's underlying string then <a href="common-microsyntaxes.html#remove-a-token-from-a-string" title="remove a token from a string">remove the given <var title="">token</var> from the underlying string</a> and stop the
   algorithm, returning false.</li>

   <li>Otherwise, if the <code><a href="#domtokenlist">DOMTokenList</a></code> object's underlying
   string is not the empty string and the last character of that
   string is not a <a href="common-microsyntaxes.html#space-character">space character</a>, then append a U+0020
   SPACE character to the end of that string.</li>

   <li>Append the value of <var title="">token</var> to the end of the
   <code><a href="#domtokenlist">DOMTokenList</a></code> object's underlying string.</li>

   <li>Return true.</li>

  </ol><p>A <code><a href="#domtokenlist">DOMTokenList</a></code> object must <dfn id="dom-tokenlist-tostring" title="dom-tokenlist-toString">stringify</dfn> to the value of the
  <code><a href="#domtokenlist">DOMTokenList</a></code> object's underlying string.</p>

  </div><h4 id="domsettabletokenlist-0"><span class="secno">2.8.4 </span>DOMSettableTokenList</h4><p>The <code><a href="#domsettabletokenlist">DOMSettableTokenList</a></code> interface is the same as the
  <code><a href="#domtokenlist">DOMTokenList</a></code> interface, except that it allows the
  underlying string to be directly changed.</p><pre class="idl">interface <dfn id="domsettabletokenlist">DOMSettableTokenList</dfn> : <a href="#domtokenlist">DOMTokenList</a> {
            attribute DOMString <a href="#dom-domsettabletokenlist-value" title="dom-DOMSettableTokenList-value">value</a>;
};</pre><dl class="domintro"><dt><var title="">tokenlist</var> . <code title="dom-DOMSettableTokenList-value"><a href="#dom-domsettabletokenlist-value">value</a></code></dt>
   <dd>
    <p>Returns the underlying string.</p>
    <p>Can be set, to change the underlying string.</p>
   </dd>

  </dl><div class="impl">

  <p>An object implementing the <code><a href="#domsettabletokenlist">DOMSettableTokenList</a></code>
  interface must act as defined for the <code><a href="#domtokenlist">DOMTokenList</a></code>
  interface, except for the <code title="dom-DOMSettableTokenList-value"><a href="#dom-domsettabletokenlist-value">value</a></code> attribute defined
  here.</p>

  <p>The <dfn id="dom-domsettabletokenlist-value" title="dom-DOMSettableTokenList-value"><code>value</code></dfn>
  attribute must return the underlying string on getting, and must
  replace the underlying string with the new value on setting.</p>

  </div><div class="impl">

  <h4 id="safe-passing-of-structured-data"><span class="secno">2.8.5 </span>Safe passing of structured data</h4>

  <p>When a user agent is required to obtain a <dfn id="structured-clone">structured
  clone</dfn> of a value, it must run the following algorithm, which
  either returns a separate value, or throws an exception.</p>

  <ol><li><p>Let <var title="">input</var> be the value being
   cloned.</p></li>

   <li><p>Let <var title="">memory</var> be an association list of
   pairs of objects, initially empty. This is used to handle duplicate
   references. In each pair of objects, one is called the
   <em>source</em> object and the other the <em>destination</em>
   object.</p></li>

   <li><p>Let <var title="">output</var> be the value resulting from
   calling the <a href="#internal-structured-cloning-algorithm">internal structured cloning algorithm</a> with
   <var title="">input</var> and <var title="">memory</var>.</p></li>

   <li><p>Return <var title="">output</var>.</p></li>

  </ol><p>The <dfn id="internal-structured-cloning-algorithm">internal structured cloning algorithm</dfn> is always
  called with two arguments, <var title="">input</var> and <var title="">memory</var>, and its behavior is as follows:</p>

  <ol><li><p>If <var title="">input</var> is the source object of a pair
   of objects in <var title="">memory</var>, then return the
   destination object in that pair of objects and abort these
   steps.</p></li>

   <li><p>If <var title="">input</var> is a primitive value, then
   return that value and abort these steps.</p></li>

   <li>

    <p>The <var title="">input</var> value is an object. Jump to the
    appropriate step below:</p>

    <dl class="switch"><dt>If <var title="">input</var> is a Boolean object</dt>

     <dd><p>Let <var title="">output</var> be a newly constructed Boolean object with the same value as <var title="">input</var>.</p></dd>

     <dt>If <var title="">input</var> is a Number object</dt>

     <dd><p>Let <var title="">output</var> be a newly constructed Number object with the same value as <var title="">input</var>.</p></dd>

     <dt>If <var title="">input</var> is a String object</dt>

     <dd><p>Let <var title="">output</var> be a newly constructed String object with the same value as <var title="">input</var>.</p></dd>

     <dt>If <var title="">input</var> is a <code>Date</code> object</dt>

     <dd><p>Let <var title="">output</var> be a newly constructed <code>Date</code> object with the same value as <var title="">input</var>.</p></dd>

     <dt>If <var title="">input</var> is a <code>RegExp</code> object</dt>

     <dd>

      <p>Let <var title="">output</var> be a newly constructed <code>RegExp</code> object with the same pattern and flags as <var title="">input</var>.</p>

      <p class="note">The value of the <code title="">lastIndex</code> property is not copied.</p>

     </dd>

     <dt>If <var title="">input</var> is a <code>ImageData</code> object</dt>

     <dd><p>Let <var title="">output</var> be a newly constructed <code>ImageData</code> object
     with the same <code title="dom-imagedata-width">width</code> and
     <code title="dom-imagedata-height">height</code> as <var title="">input</var>, and with a newly constructed
     <code>CanvasPixelArray</code> for its <code title="dom-imagedata-data">data</code> attribute, with the same
     <code title="dom-canvaspixelarray-length">length</code> and pixel
     values as the <var title="">input</var>'s.</p></dd>

     <dt>If <var title="">input</var> is a <code><a href="infrastructure.html#file">File</a></code> object</dt>

     <dd><p>Let <var title="">output</var> be a newly constructed <code><a href="infrastructure.html#file">File</a></code> object corresponding to the same underlying data.</p></dd>

     <dt>If <var title="">input</var> is a <code><a href="infrastructure.html#blob">Blob</a></code> object</dt>

     <dd><p>Let <var title="">output</var> be a newly constructed <code><a href="infrastructure.html#blob">Blob</a></code> object corresponding to the same underlying data.</p></dd>

     <dt>If <var title="">input</var> is a <code><a href="infrastructure.html#filelist">FileList</a></code> object</dt>

     <dd><p>Let <var title="">output</var> be a newly constructed <code><a href="infrastructure.html#filelist">FileList</a></code> object containing a list of newly constructed <code><a href="infrastructure.html#file">File</a></code> objects corresponding to the same underlying data as those in <var title="">input</var>, maintaining their relative order.</p></dd>

     <dt>If <var title="">input</var> is an Array object</dt>

     <dd><p>Let <var title="">output</var> be a newly constructed empty <code>Array</code> object.</p></dd>

     <dt>If <var title="">input</var> is an Object object</dt>

     <dd><p>Let <var title="">output</var> be a newly constructed empty <code title="">Object</code> object.</p></dd>

     <dt>If <var title="">input</var> is another native object type (e.g. <code>Error</code>, <code><a href="webappapis.html#function">Function</a></code>)</dt>
     <dt>If <var title="">input</var> is a host object (e.g. a DOM node)</dt>

     <dd><p>Throw a <code><a href="#data_clone_err">DATA_CLONE_ERR</a></code> exception and abort
     the overall <a href="#structured-clone">structured clone</a> algorithm.</p></dd>

    </dl></li>

   <li><p>Add a mapping from <var title="">input</var> (the source
   object) to <var title="">output</var> (the destination object) to
   <var title="">memory</var>.</p></li>

   <li>

    <p>If <var title="">input</var> is an Array object or an Object
    object, then, for each enumerable property in <var title="">input</var>, add a new property to <var title="">output</var> having the same name, and having a value
    created from invoking the <a href="#internal-structured-cloning-algorithm">internal structured cloning
    algorithm</a> recursively with the value of the property as the
    "<var title="">input</var>" argument and <var title="">memory</var> as the "<var title="">memory</var>"
    argument. The order of the properties in the <var title="">input</var> and <var title="">output</var> objects must
    be the same.</p>

    <p class="note">This does not walk the prototype chain.</p>

    <p class="note">Property descriptors, setters, getters, and
    analogous features are not copied in this process. For example,
    the property in the input could be marked as read-only, but in the
    output it would just have the default state (typically read-write,
    though that could depend on the scripting environment).</p>

   </li>

   <li><p>Return <var title="">output</var>.</p></li>

  </ol><p class="note">This algorithm preserves cycles and preserves the
  identity of duplicate objects in graphs.</p>

  </div><h4 id="domstringmap-0"><span class="secno">2.8.6 </span>DOMStringMap</h4><p>The <code><a href="#domstringmap">DOMStringMap</a></code> interface represents a set of
  name-value pairs. It exposes these using the scripting language's
  native mechanisms for property access.</p><div class="impl">

  <p>When a <code><a href="#domstringmap">DOMStringMap</a></code> object is instantiated, it is
  associated with three algorithms, one for getting the list of
  name-value pairs, one for setting names to certain values, and one
  for deleting names.</p>

  <pre class="idl">interface <dfn id="domstringmap">DOMStringMap</dfn> {
  <a href="#dom-domstringmap-nameditem" title="dom-DOMStringMap-namedItem">getter</a> DOMString (in DOMString name);
  <a href="#dom-domstringmap-setitem" title="dom-DOMStringMap-setItem">setter</a> void (in DOMString name, in DOMString value);
  <a href="#dom-domstringmap-additem" title="dom-DOMStringMap-addItem">creator</a> void (in DOMString name, in DOMString value);
  <a href="#dom-domstringmap-removeitem" title="dom-DOMStringMap-removeItem">deleter</a> void (in DOMString name);
};</pre>

  <p>The <a href="infrastructure.html#supported-property-names">supported property names</a> on a
  <code><a href="#domstringmap">DOMStringMap</a></code> object at any instant are the names of
  each pair returned from the algorithm for getting the list of
  name-value pairs at that instant.</p>

  <p>To <dfn id="dom-domstringmap-nameditem" title="dom-DOMStringMap-namedItem">determine the value of
  a named property</dfn> <var title="">name</var> in a
  <code><a href="#domstringmap">DOMStringMap</a></code>, the user agent must return the value
  component of the name-value pair whose name component is <var title="">name</var> in the list returned by the algorithm for
  getting the list of name-value pairs.</p>

  <p>To set the value of a <dfn id="dom-domstringmap-additem" title="dom-DOMStringMap-addItem">new</dfn> or <dfn id="dom-domstringmap-setitem" title="dom-DOMStringMap-setItem">existing</dfn> named property <var title="">name</var> to value <var title="">value</var>, the
  algorithm for setting names to certain values must be run, passing
  <var title="">name</var> as the name and the result of converting
  <var title="">value</var> to a <code>DOMString</code> as the
  value.</p>

  <p>To <dfn id="dom-domstringmap-removeitem" title="dom-DOMStringMap-removeItem">delete an existing
  named property</dfn> <var title="">name</var>, the algorithm for
  deleting names must be run, passing <var title="">name</var> as the
  name.</p>

  <p class="note">The <code><a href="#domstringmap">DOMStringMap</a></code> interface definition
  here is only intended for JavaScript environments. Other language
  bindings will need to define how <code><a href="#domstringmap">DOMStringMap</a></code> is to be
  implemented for those languages.</p>

  </div><div class="example">

   <p>The <code title="dom-dataset"><a href="elements.html#dom-dataset">dataset</a></code> attribute on
   elements exposes the <code title="attr-data-*"><a href="elements.html#attr-data">data-*</a></code>
   attributes on the element.</p>

   <p>Given the following fragment and elements with similar
   constructions:</p>

   <pre>&lt;img class="tower" id="tower5" data-x="12" data-y="5"
     data-ai="robotarget" data-hp="46" data-ability="flames"
     src="towers/rocket.png alt="Rocket Tower"&gt;</pre>

   <p>...one could imagine a function <code title="">splashDamage()</code> that takes some arguments, the first
   of which is the element to process:</p>

   <pre>function splashDamage(node, x, y, damage) {
  if (node.classList.contains('tower') &amp;&amp; // checking the 'class' attribute
      node.dataset.x == x &amp;&amp; // reading the 'data-x' attribute
      node.dataset.y == y) { // reading the 'data-y' attribute
    var hp = parseInt(node.dataset.hp); // reading the 'data-hp' attribute
    hp = hp - damage;
    if (hp &lt; 0) {
      hp = 0;
      node.dataset.ai = 'dead'; // setting the 'data-ai' attribute
      delete node.dataset.ability; // removing the 'data-ability' attribute
    }
    node.dataset.hp = hp; // setting the 'data-hp' attribute
  }
}</pre>

  </div><h4 id="dom-feature-strings"><span class="secno">2.8.7 </span>DOM feature strings</h4><p>DOM3 Core defines mechanisms for checking for interface support,
  and for obtaining implementations of interfaces, using <a href="http://www.w3.org/TR/DOM-Level-3-Core/core.html#DOMFeatures">feature
  strings</a>. <a href="references.html#refsDOMCORE">[DOMCORE]</a></p><p>Authors are strongly discouraged from using these, as they are
  notoriously unreliable and imprecise. Authors are encouraged to rely
  on explicit feature testing or the graceful degradation behavior
  intrinsic to some of the features in this specification.</p><div class="impl">

  <p>For historical reasons, user agents should return the true value
  when the <dfn id="hasfeature" title="hasFeature"><code>hasFeature(<var title="">feature</var>, <var title="">version</var>)</code></dfn>
  method of the <code><a href="infrastructure.html#domimplementation">DOMImplementation</a></code> interface is invoked
  with <var title="">feature</var> set to either "<code title="">HTML</code>" or "<code title="">XHTML</code>" and <var title="">version</var> set to either "<code>1.0</code>" or
  "<code>2.0</code>".</p>

  </div><h4 id="exceptions"><span class="secno">2.8.8 </span>Exceptions</h4><p>The following are <code><a href="infrastructure.html#domexception">DOMException</a></code> codes. <a href="references.html#refsDOMCORE">[DOMCORE]</a></p><ol class="brief"><li value="1"><dfn id="index_size_err"><code>INDEX_SIZE_ERR</code></dfn></li>
   <li value="2"><dfn id="domstring_size_err"><code>DOMSTRING_SIZE_ERR</code></dfn></li>
   <li value="3"><dfn id="hierarchy_request_err"><code>HIERARCHY_REQUEST_ERR</code></dfn></li>
   <li value="4"><dfn id="wrong_document_err"><code>WRONG_DOCUMENT_ERR</code></dfn></li>
   <li value="5"><dfn id="invalid_character_err"><code>INVALID_CHARACTER_ERR</code></dfn></li>
   <li value="6"><dfn id="no_data_allowed_err"><code>NO_DATA_ALLOWED_ERR</code></dfn></li>
   <li value="7"><dfn id="no_modification_allowed_err"><code>NO_MODIFICATION_ALLOWED_ERR</code></dfn></li>
   <li value="8"><dfn id="not_found_err"><code>NOT_FOUND_ERR</code></dfn></li>
   <li value="9"><dfn id="not_supported_err"><code>NOT_SUPPORTED_ERR</code></dfn></li>
   <li value="10"><dfn id="inuse_attribute_err"><code>INUSE_ATTRIBUTE_ERR</code></dfn></li>
   <li value="11"><dfn id="invalid_state_err"><code>INVALID_STATE_ERR</code></dfn></li>
   <li value="12"><dfn id="syntax_err"><code>SYNTAX_ERR</code></dfn></li>
   <li value="13"><dfn id="invalid_modification_err"><code>INVALID_MODIFICATION_ERR</code></dfn></li>
   <li value="14"><dfn id="namespace_err"><code>NAMESPACE_ERR</code></dfn></li>
   <li value="15"><dfn id="invalid_access_err"><code>INVALID_ACCESS_ERR</code></dfn></li>
   <li value="16"><dfn id="validation_err"><code>VALIDATION_ERR</code></dfn></li>
   <li value="17"><dfn id="type_mismatch_err"><code>TYPE_MISMATCH_ERR</code></dfn></li>
   <li value="18"><dfn id="security_err"><code>SECURITY_ERR</code></dfn></li> 
   <li value="19"><dfn id="network_err"><code>NETWORK_ERR</code></dfn></li> 
   <li value="20"><dfn id="abort_err"><code>ABORT_ERR</code></dfn></li> 
   <li value="21"><dfn id="url_mismatch_err"><code>URL_MISMATCH_ERR</code></dfn></li> 
   <li value="22"><dfn id="quota_exceeded_err"><code>QUOTA_EXCEEDED_ERR</code></dfn></li> 
   <li value="23"><dfn id="timeout_err"><code>TIMEOUT_ERR</code></dfn></li> 
   <li value="25"><dfn id="data_clone_err"><code>DATA_CLONE_ERR</code></dfn></li> 
  </ol><div class="impl">

  <pre class="idl">[Supplemental] exception DOMException {
  const unsigned short <a href="#url_mismatch_err">URL_MISMATCH_ERR</a> = 21;
  const unsigned short <a href="#quota_exceeded_err">QUOTA_EXCEEDED_ERR</a> = 22;
  const unsigned short <a href="#data_clone_err">DATA_CLONE_ERR</a> = 25;
};</pre>

  </div><div class="impl">

  <h4 id="garbage-collection"><span class="secno">2.8.9 </span>Garbage collection</h4>

  <p>There is an <dfn id="implied-strong-reference">implied strong reference</dfn> from any IDL
  attribute that returns a pre-existing object to that object.</p>

  <div class="example">

   <p>For example, the <code>document.location</code> attribute means
   that there is a strong reference from a <code><a href="infrastructure.html#document">Document</a></code>
   object to its <code><a href="history.html#location">Location</a></code> object. Similarly, there is
   always a strong reference from a <code><a href="infrastructure.html#document">Document</a></code> to any
   descendant nodes, and from any node to its owner
   <code><a href="infrastructure.html#document">Document</a></code>.</p>

  </div>

  </div></body></html>