HTML

15.1.1 Warnings for obsolete but conforming features

To ease the transition from HTML4 Transitional documents to the language defined in this specification, and to discourage certain features that are only allowed in very few circumstances, conformance checkers are required to warn the user when the following features are used in a document. These are generally old obsolete features that have no effect, and are allowed only to distinguish between likely mistakes (regular conformance errors) and mere vestigial markup or unusual and discouraged practices (these warnings).

The following features must be categorized as described above:

• The presence of an obsolete permitted DOCTYPE in an HTML document.

• The presence of a border attribute on an img element if its value is the string "0".

• The presence of a language attribute on a script element if its value is an ASCII case-insensitive match for the string "JavaScript" and if there is no type attribute or there is and its value is an ASCII case-insensitive match for the string "text/javascript".

• The presence of a name attribute on an a element, if its value is not the empty string.

• The presence of a maxlength attribute on an input element whose type attribute is in the Number state.

• The presence of a size attribute on an input element whose type attribute is in the Number state.

Conformance checkers must distinguish between pages that have no conformance errors and have none of these obsolete features, and pages that have no conformance errors but do have some of these obsolete features.

For example, a validator could report some pages as "Valid HTML" and others as "Valid HTML with warnings".

15.3 Requirements for implementations

15.3.1 The applet element

The applet element is a Java-specific variant of the embed element. The applet element is now obsoleted so that all extension frameworks (Java, .NET, Flash, etc) are handled in a consistent manner.

When the element is still in the stack of open elements of an HTML parser or XML parser, and when the element is not in a Document, and when the element's document is not fully active, and when the element's Document's browsing context had its sandboxed plugins browsing context flag when that Document was created, and when the element has an ancestor media element, and when the element has an ancestor object element that is not showing its fallback content, and when no Java Language runtime plugin is available, and when one is available but it is disabled, the element represents its contents.

Otherwise, the user agent should instantiate a Java Language runtime plugin, and should pass the names and values of all the attributes on the element, in the order they were added to the element, with the attributes added by the parser being ordered in source order, and then a parameter named "PARAM" whose value is null, and then all the names and values of parameters given by param elements that are children of the applet element, in tree order, to the plugin used. If the plugin supports a scriptable interface, the HTMLAppletElement object representing the element should expose that interface. The applet element represents the plugin.

The applet element is unaffected by the CSS 'display' property. The Java Language runtime is instantiated even if the element is hidden with a 'display:none' CSS style.

The applet element must implement the HTMLAppletElement interface.

interface HTMLAppletElement : HTMLElement {
           attribute DOMString align;
           attribute DOMString alt;
           attribute DOMString archive;
           attribute DOMString code;
           attribute DOMString codeBase;
           attribute DOMString height;
           attribute unsigned long hspace;
           attribute DOMString name;
           attribute DOMString _object; // the underscore is not part of the identifier 
           attribute unsigned long vspace;
           attribute DOMString width;
};

The align, alt, archive, code, height, hspace, name, object, vspace, and width IDL attributes must reflect the respective content attributes of the same name. For the purposes of reflection, the applet element's object content attribute is defined as containing a URL.

The codeBase IDL attribute must reflect the codebase content attribute, which for the purposes of reflection is defined as containing a URL.

15.3.2 The marquee element

The marquee element is a presentational element that animates content. CSS transitions and animations are a more appropriate mechanism.

The task source for tasks mentioned in this section is the DOM manipulation task source.

The marquee element must implement the HTMLMarqueeElement interface.

interface HTMLMarqueeElement : HTMLElement {
           attribute DOMString behavior;
           attribute DOMString bgColor;
           attribute DOMString direction;
           attribute DOMString height;
           attribute unsigned long hspace;
           attribute long loop;
           attribute unsigned long scrollAmount;
           attribute unsigned long scrollDelay;
           attribute boolean trueSpeed;
           attribute unsigned long vspace;
           attribute DOMString width;

  [TreatNonCallableAsNull] attribute Function? onbounce;
  [TreatNonCallableAsNull] attribute Function? onfinish;
  [TreatNonCallableAsNull] attribute Function? onstart;

  void start();
  void stop();
};

A marquee element can be turned on or turned off. When it is created, it is turned on.

When the start() method is called, the marquee element must be turned on.

When the stop() method is called, the marquee element must be turned off.

When a marquee element is created, the user agent must queue a task to fire a simple event named start at the element.

The behavior content attribute on marquee elements is an enumerated attribute with the following keywords (all non-conforming):

The missing value default is the scroll state.

The direction content attribute on marquee elements is an enumerated attribute with the following keywords (all non-conforming):

The missing value default is the left state.

The truespeed content attribute on marquee elements is a boolean attribute.

A marquee element has a marquee scroll interval, which is obtained as follows:

1. If the element has a scrolldelay attribute, and parsing its value using the rules for parsing non-negative integers does not return an error, then let delay be the parsed value. Otherwise, let delay be 85.

2. If the element does not have a truespeed attribute, and the delay value is less than 60, then let delay be 60 instead.

3. The marquee scroll interval is delay, interpreted in milliseconds.

A marquee element has a marquee scroll distance, which, if the element has a scrollamount attribute, and parsing its value using the rules for parsing non-negative integers does not return an error, is the parsed value interpreted in CSS pixels, and otherwise is 6 CSS pixels.

A marquee element has a marquee loop count, which, if the element has a loop attribute, and parsing its value using the rules for parsing integers does not return an error or a number less than 1, is the parsed value, and otherwise is −1.

The loop IDL attribute, on getting, must return the element's marquee loop count; and on setting, if the new value is different than the element's marquee loop count and either greater than zero or equal to −1, must set the element's loop content attribute (adding it if necessary) to the valid integer that represents the new value. (Other values are ignored.)

A marquee element also has a marquee current loop index, which is zero when the element is created.

The rendering layer will occasionally increment the marquee current loop index, which must cause the following steps to be run:

1. If the marquee loop count is −1, then abort these steps.

2. Increment the marquee current loop index by one.

3. If the marquee current loop index is now equal to or greater than the element's marquee loop count, turn off the marquee element and queue a task to fire a simple event named finish at the marquee element.

   Otherwise, if the behavior attribute is in the alternate state, then queue a task to fire a simple event named bounce at the marquee element.

   Otherwise, queue a task to fire a simple event named start at the marquee element.

The following are the event handlers (and their corresponding event handler event types) that must be supported, as content and IDL attributes, by marquee elements:

The behavior, direction, height, hspace, vspace, and width IDL attributes must reflect the respective content attributes of the same name.

The bgColor IDL attribute must reflect the bgcolor content attribute.

The scrollAmount IDL attribute must reflect the scrollamount content attribute. The default value is 6.

The scrollDelay IDL attribute must reflect the scrolldelay content attribute. The default value is 85.

The trueSpeed IDL attribute must reflect the truespeed content attribute.

15.3.3 Frames

The frameset element acts as the body element in documents that use frames.

The frameset element must implement the HTMLFrameSetElement interface.

interface HTMLFrameSetElement : HTMLElement {
           attribute DOMString cols;
           attribute DOMString rows;
  [TreatNonCallableAsNull] attribute Function? onafterprint;
  [TreatNonCallableAsNull] attribute Function? onbeforeprint;
  [TreatNonCallableAsNull] attribute Function? onbeforeunload;
  [TreatNonCallableAsNull] attribute Function? onblur;
  [TreatNonCallableAsNull] attribute Function? onerror;
  [TreatNonCallableAsNull] attribute Function? onfocus;
  [TreatNonCallableAsNull] attribute Function? onhashchange;
  [TreatNonCallableAsNull] attribute Function? onload;
  [TreatNonCallableAsNull] attribute Function? onmessage;
  [TreatNonCallableAsNull] attribute Function? onoffline;
  [TreatNonCallableAsNull] attribute Function? ononline;
  [TreatNonCallableAsNull] attribute Function? onpagehide;
  [TreatNonCallableAsNull] attribute Function? onpageshow;
  [TreatNonCallableAsNull] attribute Function? onpopstate;
  [TreatNonCallableAsNull] attribute Function? onresize;
  [TreatNonCallableAsNull] attribute Function? onscroll;
  [TreatNonCallableAsNull] attribute Function? onstorage;
  [TreatNonCallableAsNull] attribute Function? onunload;
};

The cols and rows IDL attributes of the frameset element must reflect the respective content attributes of the same name.

The frameset element must support the following event handler content attributes exposing the event handlers of the Window object:

• onafterprint
• onbeforeprint
• onbeforeunload
• onblur
• onerror
• onfocus
• onhashchange
• onload
• onmessage
• onoffline
• ononline
• onpagehide
• onpageshow
• onpopstate
• onresize
• onscroll
• onstorage
• onunload

The DOM interface also exposes event handler IDL attributes that mirror those on the Window element.

The onblur, onerror, onfocus, onload, and onscroll event handler IDL attributes of the Window object, exposed on the frameset element, shadow the generic event handler IDL attributes with the same names normally supported by HTML elements.

The frame element defines a nested browsing context similar to the iframe element, but rendered within a frameset element.

When the browsing context is created, if a src attribute is present, the user agent must resolve the value of that attribute, relative to the element, and if that is successful, must then navigate the element's browsing context to the resulting absolute URL, with replacement enabled, and with the frame element's document's browsing context as the source browsing context.

Whenever the src attribute is set, the user agent must resolve the value of that attribute, relative to the element, and if that is successful, the nested browsing context must be navigated to the resulting absolute URL, with the frame element's document's browsing context as the source browsing context.

When the browsing context is created, if a name attribute is present, the browsing context name must be set to the value of this attribute; otherwise, the browsing context name must be set to the empty string.

Whenever the name attribute is set, the nested browsing context's name must be changed to the new value. If the attribute is removed, the browsing context name must be set to the empty string.

When content loads in a frame, after any load events are fired within the content itself, the user agent must queue a task to fire a simple event named load at the frame element. When content fails to load (e.g. due to a network error), then the user agent must queue a task to fire a simple event named error at the element instead.

The task source for the tasks above is the DOM manipulation task source.

When there is an active parser in the frame, and when anything in the frame is delaying the load event of the frame's browsing context's active document, the frame must delay the load event of its document.

The frame element must implement the HTMLFrameElement interface.

interface HTMLFrameElement : HTMLElement {
           attribute DOMString name;
           attribute DOMString scrolling;
           attribute DOMString src;
           attribute DOMString frameBorder;
           attribute DOMString longDesc;
           attribute boolean noResize;
  readonly attribute Document? contentDocument;
  readonly attribute WindowProxy? contentWindow;

  [TreatNullAs=EmptyString] attribute DOMString marginHeight;
  [TreatNullAs=EmptyString] attribute DOMString marginWidth;
};

The name, scrolling, and src IDL attributes of the frame element must reflect the respective content attributes of the same name.

The frameBorder IDL attribute of the frame element must reflect the element's frameborder content attribute.

The longDesc IDL attribute of the frame element must reflect the element's longdesc content attribute, which for the purposes of reflection is defined as containing a URL.

The noResize IDL attribute of the frame element must reflect the element's noresize content attribute.

The contentDocument IDL attribute of the frame element must return the Document object of the active document of the frame element's nested browsing context.

The contentWindow IDL attribute must return the WindowProxy object of the frame element's nested browsing context.

The marginHeight IDL attribute of the frame element must reflect the element's marginheight content attribute.

The marginWidth IDL attribute of the frame element must reflect the element's marginwidth content attribute.

15.3.4 Other elements, attributes and APIs

User agents must treat acronym elements in a manner equivalent to abbr elements in terms of semantics and for purposes of rendering.

partial interface HTMLAnchorElement {
           attribute DOMString coords;
           attribute DOMString charset;
           attribute DOMString name;
           attribute DOMString rev;
           attribute DOMString shape;
};

The coords, charset, name, rev, and shape IDL attributes of the a element must reflect the respective content attributes of the same name.

partial interface HTMLAreaElement {
           attribute boolean noHref;
};

The noHref IDL attribute of the area element must reflect the element's nohref content attribute.

The basefont element must implement the HTMLBaseFontElement interface.

interface HTMLBaseFontElement : HTMLElement {
           attribute DOMString color;
           attribute DOMString face;
           attribute long size; 
};

The color, face, and size IDL attributes of the basefont element must reflect the respective content attributes of the same name.

partial interface HTMLBodyElement {
  [TreatNullAs=EmptyString] attribute DOMString text;
  [TreatNullAs=EmptyString] attribute DOMString link;
  [TreatNullAs=EmptyString] attribute DOMString vLink;
  [TreatNullAs=EmptyString] attribute DOMString aLink;
  [TreatNullAs=EmptyString] attribute DOMString bgColor;
                            attribute DOMString background;
};

The text IDL attribute of the body element must reflect the element's text content attribute.

The link IDL attribute of the body element must reflect the element's link content attribute.

The aLink IDL attribute of the body element must reflect the element's alink content attribute.

The vLink IDL attribute of the body element must reflect the element's vlink content attribute.

The bgColor IDL attribute of the body element must reflect the element's bgcolor content attribute.

The background IDL attribute of the body element must reflect the element's background content attribute. (The background content is not defined to contain a URL, despite rules regarding its handling in the rendering section above.)

partial interface HTMLBRElement {
           attribute DOMString clear;
};

The clear IDL attribute of the br element must reflect the content attribute of the same name.

partial interface HTMLTableCaptionElement {
           attribute DOMString align;
};

The align IDL attribute of the caption element must reflect the content attribute of the same name.

partial interface HTMLTableColElement {
           attribute DOMString align;
           attribute DOMString ch;
           attribute DOMString chOff;
           attribute DOMString vAlign;
           attribute DOMString width;
};

The align and width IDL attributes of the col element must reflect the respective content attributes of the same name.

The ch IDL attribute of the col element must reflect the element's char content attribute.

The chOff IDL attribute of the col element must reflect the element's charoff content attribute.

The vAlign IDL attribute of the col element must reflect the element's valign content attribute.

User agents must treat dir elements in a manner equivalent to ul elements in terms of semantics and for purposes of rendering.

The dir element must implement the HTMLDirectoryElement interface.

interface HTMLDirectoryElement : HTMLElement {
           attribute boolean compact;
};

The compact IDL attribute of the dir element must reflect the content attribute of the same name.

partial interface HTMLDivElement {
           attribute DOMString align;
};

The align IDL attribute of the div element must reflect the content attribute of the same name.

partial interface HTMLDListElement {
           attribute boolean compact;
};

The compact IDL attribute of the dl element must reflect the content attribute of the same name.

partial interface HTMLEmbedElement {
           attribute DOMString align;
           attribute DOMString name;
};

The name and align IDL attributes of the embed element must reflect the respective content attributes of the same name.

The font element must implement the HTMLFontElement interface.

interface HTMLFontElement : HTMLElement {
  [TreatNullAs=EmptyString] attribute DOMString color;
                            attribute DOMString face;
                            attribute DOMString size; 
};

The color, face, and size IDL attributes of the font element must reflect the respective content attributes of the same name.

partial interface HTMLHeadingElement {
           attribute DOMString align;
};

The align IDL attribute of the h1–h6 elements must reflect the content attribute of the same name.

The profile IDL attribute on head elements (with the HTMLHeadElement interface) is intentionally omitted. Unless so required by another applicable specification, implementations would therefore not support this attribute. (It is mentioned here as it was defined in a previous version of the DOM specifications.)

partial interface HTMLHRElement {
           attribute DOMString align;
           attribute DOMString color;
           attribute boolean noShade;
           attribute DOMString size;
           attribute DOMString width;
};

The align, color, size, and width IDL attributes of the hr element must reflect the respective content attributes of the same name.

The noShade IDL attribute of the hr element must reflect the element's noshade content attribute.

partial interface HTMLHtmlElement {
           attribute DOMString version;
};

The version IDL attribute of the html element must reflect the content attribute of the same name.

partial interface HTMLIFrameElement {
           attribute DOMString align;
           attribute DOMString scrolling;
           attribute DOMString frameBorder;
           attribute DOMString longDesc;

  [TreatNullAs=EmptyString] attribute DOMString marginHeight;
  [TreatNullAs=EmptyString] attribute DOMString marginWidth;
};

The align and scrolling IDL attributes of the iframe element must reflect the respective content attributes of the same name.

The frameBorder IDL attribute of the iframe element must reflect the element's frameborder content attribute.

The longDesc IDL attribute of the iframe element must reflect the element's longdesc content attribute, which for the purposes of reflection is defined as containing a URL.

The marginHeight IDL attribute of the iframe element must reflect the element's marginheight content attribute.

The marginWidth IDL attribute of the iframe element must reflect the element's marginwidth content attribute.

partial interface HTMLImageElement {
           attribute DOMString name;
           attribute DOMString align;
           attribute unsigned long hspace;
           attribute unsigned long vspace;
           attribute DOMString longDesc;

  [TreatNullAs=EmptyString] attribute DOMString border;
};

The name, align, border, hspace, and vspace IDL attributes of the img element must reflect the respective content attributes of the same name.

The longDesc IDL attribute of the img element must reflect the element's longdesc content attribute, which for the purposes of reflection is defined as containing a URL.

partial interface HTMLInputElement {
           attribute DOMString align;
           attribute DOMString useMap;
};

The align IDL attribute of the input element must reflect the content attribute of the same name.

The useMap IDL attribute of the input element must reflect the element's usemap content attribute.

partial interface HTMLLegendElement {
           attribute DOMString align;
};

The align IDL attribute of the legend element must reflect the content attribute of the same name.

partial interface HTMLLIElement {
           attribute DOMString type;
};

The type IDL attribute of the li element must reflect the content attribute of the same name.

partial interface HTMLLinkElement {
           attribute DOMString charset;
           attribute DOMString rev;
           attribute DOMString target;
};

The charset, rev, and target IDL attributes of the link element must reflect the respective content attributes of the same name.

User agents must treat listing elements in a manner equivalent to pre elements in terms of semantics and for purposes of rendering.

partial interface HTMLMenuElement {
           attribute boolean compact;
};

The compact IDL attribute of the menu element must reflect the content attribute of the same name.

partial interface HTMLMetaElement {
           attribute DOMString scheme;
};

User agents may treat the scheme content attribute on the meta element as an extension of the element's name content attribute when processing a meta element with a name attribute whose value is one that the user agent recognizes as supporting the scheme attribute.

User agents are encouraged to ignore the scheme attribute and instead process the value given to the metadata name as if it had been specified for each expected value of the scheme attribute.

<!-- this markup is invalid -->
<meta name="eGMS.subject.keyword" scheme="LGCL" content="Abandoned vehicles">
<meta name="eGMS.subject.keyword" scheme="ORLY" content="Mah car: kthxbye">

<meta name="eGMS.subject.keyword" content="Abandoned vehicles">
<meta name="eGMS.subject.keyword" content="Mah car: kthxbye">

The scheme IDL attribute of the meta element must reflect the content attribute of the same name.

partial interface HTMLObjectElement {
           attribute DOMString align;
           attribute DOMString archive;
           attribute DOMString code;
           attribute boolean declare;
           attribute unsigned long hspace;
           attribute DOMString standby;
           attribute unsigned long vspace;
           attribute DOMString codeBase;
           attribute DOMString codeType;

  [TreatNullAs=EmptyString] attribute DOMString border;
};

The align, archive, border, code, declare, hspace, standby, and vspace IDL attributes of the object element must reflect the respective content attributes of the same name.

The codeBase IDL attribute of the object element must reflect the element's codebase content attribute, which for the purposes of reflection is defined as containing a URL.

The codeType IDL attribute of the object element must reflect the element's codetype content attribute.

partial interface HTMLOListElement {
           attribute boolean compact;
};

The compact IDL attribute of the ol element must reflect the content attribute of the same name.

partial interface HTMLParagraphElement {
           attribute DOMString align;
};

The align IDL attribute of the p element must reflect the content attribute of the same name.

partial interface HTMLParamElement {
           attribute DOMString type;
           attribute DOMString valueType;
};

The type IDL attribute of the param element must reflect the content attribute of the same name.

The valueType IDL attribute of the param element must reflect the element's valuetype content attribute.

User agents must treat plaintext elements in a manner equivalent to pre elements in terms of semantics and for purposes of rendering. (The parser has special behavior for this element, though.)

partial interface HTMLPreElement {
           attribute long width;
};

The width IDL attribute of the pre element must reflect the content attribute of the same name.

partial interface HTMLScriptElement {
           attribute DOMString event;
           attribute DOMString htmlFor;
};

The event and htmlFor IDL attributes of the script element must return the empty string on getting, and do nothing on setting.

partial interface HTMLTableElement {
           attribute DOMString align;
           attribute DOMString frame;
           attribute DOMString rules;
           attribute DOMString summary;
           attribute DOMString width;

  [TreatNullAs=EmptyString] attribute DOMString bgColor;
  [TreatNullAs=EmptyString] attribute DOMString cellPadding;
  [TreatNullAs=EmptyString] attribute DOMString cellSpacing;
};

The align, frame, summary, rules, and width, IDL attributes of the table element must reflect the respective content attributes of the same name.

The bgColor IDL attribute of the table element must reflect the element's bgcolor content attribute.

The cellPadding IDL attribute of the table element must reflect the element's cellpadding content attribute.

The cellSpacing IDL attribute of the table element must reflect the element's cellspacing content attribute.

partial interface HTMLTableSectionElement {
           attribute DOMString align;
           attribute DOMString ch;
           attribute DOMString chOff;
           attribute DOMString vAlign;
};

The align IDL attribute of the tbody, thead, and tfoot elements must reflect the content attribute of the same name.

The ch IDL attribute of the tbody, thead, and tfoot elements must reflect the elements' char content attributes.

The chOff IDL attribute of the tbody, thead, and tfoot elements must reflect the elements' charoff content attributes.

The vAlign IDL attribute of the tbody, thead, and tfoot element must reflect the elements' valign content attributes.

partial interface HTMLTableCellElement {
           attribute DOMString abbr;
           attribute DOMString align;
           attribute DOMString axis;
           attribute DOMString height;
           attribute DOMString width;

           attribute DOMString ch;
           attribute DOMString chOff;
           attribute boolean noWrap;
           attribute DOMString vAlign;

  [TreatNullAs=EmptyString] attribute DOMString bgColor;
};

The abbr, align, axis, height, and width IDL attributes of the td and th elements must reflect the respective content attributes of the same name.

The ch IDL attribute of the td and th elements must reflect the elements' char content attributes.

The chOff IDL attribute of the td and th elements must reflect the elements' charoff content attributes.

The noWrap IDL attribute of the td and th elements must reflect the elements' nowrap content attributes.

The vAlign IDL attribute of the td and th element must reflect the elements' valign content attributes.

The bgColor IDL attribute of the td and th elements must reflect the elements' bgcolor content attributes.

partial interface HTMLTableRowElement {
           attribute DOMString align;
           attribute DOMString ch;
           attribute DOMString chOff;
           attribute DOMString vAlign;

  [TreatNullAs=EmptyString] attribute DOMString bgColor;
};

The align IDL attribute of the tr element must reflect the content attribute of the same name.

The ch IDL attribute of the tr element must reflect the element's char content attribute.

The chOff IDL attribute of the tr element must reflect the element's charoff content attribute.

The vAlign IDL attribute of the tr element must reflect the element's valign content attribute.

The bgColor IDL attribute of the tr element must reflect the element's bgcolor content attribute.

partial interface HTMLUListElement {
           attribute boolean compact;
           attribute DOMString type;
};

The compact and type IDL attributes of the ul element must reflect the respective content attributes of the same name.

User agents must treat xmp elements in a manner equivalent to pre elements in terms of semantics and for purposes of rendering. (The parser has special behavior for this element though.)

The bgsound, isindex, multicol, nextid, rb, and spacer elements must use the HTMLUnknownElement interface.

partial interface Document {
  [TreatNullAs=EmptyString] attribute DOMString fgColor;
  [TreatNullAs=EmptyString] attribute DOMString linkColor;
  [TreatNullAs=EmptyString] attribute DOMString vlinkColor;
  [TreatNullAs=EmptyString] attribute DOMString alinkColor;
  [TreatNullAs=EmptyString] attribute DOMString bgColor;

  readonly attribute HTMLCollection anchors;
  readonly attribute HTMLCollection applets;

  void clear();

  readonly attribute HTMLAllCollection all;
};

The attributes of the Document object listed in the first column of the following table must reflect the content attribute on the body element with the name given in the corresponding cell in the second column on the same row, if the body element is a body element (as opposed to a frameset element). When there is no body element or if it is a frameset element, the attributes must instead return the empty string on getting and do nothing on setting.

The anchors attribute must return an HTMLCollection rooted at the Document node, whose filter matches only a elements with name attributes.

The applets attribute must return an HTMLCollection rooted at the Document node, whose filter matches only applet elements.

The clear() method must do nothing.

The all attribute must return an HTMLAllCollection rooted at the Document node, whose filter matches all elements.

The object returned for all has several unusual behaviors:

• The user agent must act as if the ToBoolean() operator in JavaScript converts the object returned for all to the false value.

• The user agent must act as if, for the purposes of the == and != operators in JavaScript, the object returned for all is equal to the undefined value.

• The user agent must act such that the typeof operator in JavaScript returns the string undefined when applied to the object returned for all.

These requirements are a willful violation of the JavaScript specification current at the time of writing (ECMAScript edition 5). The JavaScript specification requires that the ToBoolean() operator convert all objects to the true value, and does not have provisions for objects acting as if they were undefined for the purposes of certain operators. This violation is motivated by a desire for compatibility with two classes of legacy content: one that uses the presence of document.all as a way to detect legacy user agents, and one that only supports those legacy user agents and uses the document.all object without testing for its presence first. [ECMA262]