This is a snapshot of an early working draft and has therefore been superseded by the HTML standard.

This document will not be further updated.

HTML5

Draft Standard — Call For Comments — 27 October 2009

2.5 URLs

2.5.1 Terminology

A URL is a string used to identify a resource.

A URL is a valid URL if it is a valid Web address as defined by the Web addresses specification. [WEBADDRESSES]

A URL is an absolute URL if it is an absolute Web address as defined by the Web addresses specification. [WEBADDRESSES]

To parse a URL url into its component parts, the user agent must use the parse a Web address algorithm defined by the Web addresses specification. [WEBADDRESSES]

Parsing a URL results in the following components, again as defined by the Web addresses specification:

To resolve a URL to an absolute URL relative to either another absolute URL or an element, the user agent must use the resolve a Web address algorithm defined by the Web addresses specification. [WEBADDRESSES]

The document base URL of a Document object is the absolute URL obtained by running these substeps:

  1. Let fallback base url be the document's address.

  2. If fallback base url is about:blank, and the Document's browsing context has a creator browsing context, then let fallback base url be the document base URL of the creator Document instead.

  3. If there is no base element that is both a child of the head element and has an href attribute, then the document base URL is fallback base url.

  4. Otherwise, let url be the value of the href attribute of the first such element.

  5. Resolve url relative to fallback base url (thus, the base href attribute isn't affected by xml:base attributes).

  6. The document base URL is the result of the previous step if it was successful; otherwise it is fallback base url.

This specification defines the URL about:legacy-compat as a reserved, though unresolvable, about: URI. [ABOUT]

The term "URL" in this specification is used in a manner distinct from the precise technical meaning it is given in RFC 3986. Readers familiar with that RFC will find it easier to read this specification if they pretend the term "URL" as used herein is really called something else altogether. This is a willful violation of RFC 3986. [RFC3986]

2.5.2 Dynamic changes to base URLs

When an xml:base attribute changes, the attribute's element, and all descendant elements, are affected by a base URL change.

When a document's document base URL changes, all elements in that document are affected by a base URL change.

When an element is moved from one document to another, if the two documents have different base URLs, then that element and all its descendants are affected by a base URL change.

When an element is affected by a base URL change, it must act as described in the following list:

If the element is a hyperlink element

If the absolute URL identified by the hyperlink is being shown to the user, or if any data derived from that URL is affecting the display, then the href attribute should be re-resolved relative to the element and the UI updated appropriately.

For example, the CSS :link/:visited pseudo-classes might have been affected.

If the hyperlink has a ping attribute and its absolute URL(s) are being shown to the user, then the ping attribute's tokens should be re-resolved relative to the element and the UI updated appropriately.

If the element is a q, blockquote, section, article, ins, or del element with a cite attribute

If the absolute URL identified by the cite attribute is being shown to the user, or if any data derived from that URL is affecting the display, then the URL should be re-resolved relative to the element and the UI updated appropriately.

Otherwise

The element is not directly affected.

Changing the base URL doesn't affect the image displayed by img elements, although subsequent accesses of the src IDL attribute from script will return a new absolute URL that might no longer correspond to the image being shown.

2.5.3 Interfaces for URL manipulation

An interface that has a complement of URL decomposition IDL attributes will have seven attributes with the following definitions:

           attribute DOMString protocol;
           attribute DOMString host;
           attribute DOMString hostname;
           attribute DOMString port;
           attribute DOMString pathname;
           attribute DOMString search;
           attribute DOMString hash;
o . protocol [ = value ]

Returns the current scheme of the underlying URL.

Can be set, to change the underlying URL's scheme.

o . host [ = value ]

Returns the current host and port (if it's not the default port) in the underlying URL.

Can be set, to change the underlying URL's host and port.

The host and the port are separated by a colon. The port part, if omitted, will be assumed to be the current scheme's default port.

o . hostname [ = value ]

Returns the current host in the underlying URL.

Can be set, to change the underlying URL's host.

o . port [ = value ]

Returns the current port in the underlying URL.

Can be set, to change the underlying URL's port.

o . pathname [ = value ]

Returns the current path in the underlying URL.

Can be set, to change the underlying URL's path.

o . search [ = value ]

Returns the current query component in the underlying URL.

Can be set, to change the underlying URL's query component.

o . hash [ = value ]

Returns the current fragment identifier in the underlying URL.

Can be set, to change the underlying URL's fragment identifier.


The attributes defined to be URL decomposition IDL attributes must act as described for the attributes with the same corresponding names in this section.

In addition, an interface with a complement of URL decomposition IDL attributes will define an input, which is a URL that the attributes act on, and a common setter action, which is a set of steps invoked when any of the attributes' setters are invoked.

The seven URL decomposition IDL attributes have similar requirements.

On getting, if the input is an absolute URL that fulfills the condition given in the "getter condition" column corresponding to the attribute in the table below, the user agent must return the part of the input URL given in the "component" column, with any prefixes specified in the "prefix" column appropriately added to the start of the string and any suffixes specified in the "suffix" column appropriately added to the end of the string. Otherwise, the attribute must return the empty string.

On setting, the new value must first be mutated as described by the "setter preprocessor" column, then mutated by %-escaping any characters in the new value that are not valid in the relevant component as given by the "component" column. Then, if the input is an absolute URL and the resulting new value fulfills the condition given in the "setter condition" column, the user agent must make a new string output by replacing the component of the URL given by the "component" column in the input URL with the new value; otherwise, the user agent must let output be equal to the input. Finally, the user agent must invoke the common setter action with the value of output.

When replacing a component in the URL, if the component is part of an optional group in the URL syntax consisting of a character followed by the component, the component (including its prefix character) must be included even if the new value is the empty string.

The previous paragraph applies in particular to the ":" before a <port> component, the "?" before a <query> component, and the "#" before a <fragment> component.

For the purposes of the above definitions, URLs must be parsed using the URL parsing rules defined in this specification.

Attribute Component Getter Condition Prefix Suffix Setter Preprocessor Setter Condition
protocol <scheme> U+003A COLON (:) Remove all trailing U+003A COLON characters (:) The new value is not the empty string
host <hostport> input is hierarchical and uses a server-based naming authority The new value is not the empty string and input is hierarchical and uses a server-based naming authority
hostname <host> input is hierarchical and uses a server-based naming authority Remove all leading U+002F SOLIDUS characters (/) The new value is not the empty string and input is hierarchical and uses a server-based naming authority
port <port> input is hierarchical, uses a server-based naming authority, and contained a <port> component (possibly an empty one) Remove any characters in the new value that are not in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the resulting string is empty, set it to a single U+0030 DIGIT ZERO character (0). input is hierarchical and uses a server-based naming authority
pathname <path> input is hierarchical If it has no leading U+002F SOLIDUS character (/), prepend a U+002F SOLIDUS character (/) to the new value input is hierarchical
search <query> input is hierarchical, and contained a <query> component (possibly an empty one) U+003F QUESTION MARK (?) Remove one leading U+003F QUESTION MARK character (?), if any input is hierarchical
hash <fragment> input contained a <fragment> component (possibly an empty one) U+0023 NUMBER SIGN (#) Remove one leading U+0023 NUMBER SIGN character (#), if any

The table below demonstrates how the getter condition for search results in different results depending on the exact original syntax of the URL:

Input URL search value Explanation
http://example.com/ empty string No <query> component in input URL.
http://example.com/? ? There is a <query> component, but it is empty. The question mark in the resulting value is the prefix.
http://example.com/?test ?test The <query> component has the value "test".
http://example.com/?test# ?test The (empty) <fragment> component is not part of the <query> component.

2.6 Fetching resources

When a user agent is to fetch a resource, optionally from an origin origin, the following steps must be run:

  1. If the resource is identified by the URL about:blank, then return the empty string and abort these steps.

  2. Generate the address of the resource from which Request-URIs are obtained as required by HTTP for the Referer (sic) header from the document's current address of the appropriate Document as given by the following list. [HTTP]

    When navigating
    The active document of the source browsing context.
    When fetching resources for an element
    The element's Document.
    When fetching resources in response to a call to an API
    The active document of the browsing context of the first script.

    Remove any <fragment> component from the generated address of the resource from which Request-URIs are obtained.

  3. Perform the remaining steps asynchronously.

  4. If the resource is identified by an absolute URL, and the resource is to be obtained using an idempotent action (such as an HTTP GET or equivalent), and it is already being downloaded for other reasons (e.g. another invocation of this algorithm), and this request would be identical to the previous one (e.g. same Accept and Origin headers), and the user agent is configured such that it is to reuse the data from the existing download instead of initiating a new one, then use the results of the existing download instead of starting a new one.

    Otherwise, at a time convenient to the user and the user agent, download (or otherwise obtain) the resource, applying the semantics of the relevant specifications (e.g. performing an HTTP GET or POST operation, or reading the file from disk, following redirects, dereferencing javascript: URLs, etc).

    For the purposes of the Referer (sic) header, use the address of the resource from which Request-URIs are obtained generated in the earlier step.

    For the purposes of the Origin header, if the fetching algorithm was explicitly initiated from an origin, then the origin that initiated the HTTP request is origin. Otherwise, this is a request from a "privacy-sensitive" context. [ORIGIN]

  5. If there are cookies to be set, then the user agent must run the following substeps:

    1. Wait until ownership of the storage mutex can be taken by this instance of the fetching algorithm.

    2. Take ownership of the storage mutex.

    3. Update the cookies. [COOKIES]

    4. Release the storage mutex so that it is once again free.

  6. When the resource is available, or if there is an error of some description, queue a task that uses the resource as appropriate. If the resource can be processed incrementally, as, for instance, with a progressively interlaced JPEG or an HTML file, additional tasks may be queued to process the data as it is downloaded. The task source for these tasks is the networking task source.

If the user agent can determine the actual length of the resource being fetched for an instance of this algorithm, and if that length is finite, then that length is the file's size. Otherwise, the subject of the algorithm (that is, the resource being fetched) has no known size. (For example, the HTTP Content-Length header might provide this information.)

The user agent must also keep track of the number of bytes downloaded for each instance of this algorithm. This number must exclude any out-of-band metadata, such as HTTP headers.

The application cache processing model introduces some changes to the networking model to handle the returning of cached resources.

The navigation processing model handles redirects itself, overriding the redirection handling that would be done by the fetching algorithm.

Whether the type sniffing rules apply to the fetched resource depends on the algorithm that invokes the rules — they are not always applicable.

2.6.1 Protocol concepts

User agents can implement a variety of transfer protocols, but this specification mostly defines behavior in terms of HTTP. [HTTP]

The HTTP GET method is equivalent to the default retrieval action of the protocol. For example, RETR in FTP. Such actions are idempotent and safe, in HTTP terms.

The HTTP response codes are equivalent to statuses in other protocols that have the same basic meanings. For example, a "file not found" error is equivalent to a 404 code, a server error is equivalent to a 5xx code, and so on.

The HTTP headers are equivalent to fields in other protocols that have the same basic meaning. For example, the HTTP authentication headers are equivalent to the authentication aspects of the FTP protocol.

Anything in this specification that refers to HTTP also applies to HTTP-over-TLS, as represented by URLs representing the https scheme.

User agents should report certificate errors to the user and must either refuse to download resources sent with erroneous certificates or must act as if such resources were in fact served with no encryption.

User agents should warn the user that there is a potential problem whenever the user visits a page that the user has previously visited, if the page uses less secure encryption on the second visit.

Not doing so can result in users not noticing man-in-the-middle attacks.

If a user connects to a server with a self-signed certificate, the user agent could allow the connection but just act as if there had been no encryption. If the user agent instead allowed the user to override the problem and then displayed the page as if it was fully and safely encrypted, the user could be easily tricked into accepting man-in-the-middle connections.

If a user connects to a server with full encryption, but the page then refers to an external resource that has an expired certificate, then the user agent will act as if the resource was unavailable, possibly also reporting the problem to the user. If the user agent instead allowed the resource to be used, then an attacker could just look for "secure" sites that used resources from a different host and only apply man-in-the-middle attacks to that host, for example taking over scripts in the page.

If a user bookmarks a site that uses a CA-signed certificate, and then later revisits that site directly but the site has started using a self-signed certificate, the user agent could warn the user that a man-in-the-middle attack is likely underway, instead of simply acting as if the page was not encrypted.

2.6.3 Determining the type of a resource

The Content-Type metadata of a resource must be obtained and interpreted in a manner consistent with the requirements of the Content-Type Processing Model specification. [MIMESNIFF]

The algorithm for extracting an encoding from a Content-Type, given a string s, is given in the Content-Type Processing Model specification. It either returns an encoding or nothing. [MIMESNIFF]

The sniffed type of a resource must be found in a manner consistent with the requirements given in the Content-Type Processing Model specification for finding that sniffed type. [MIMESNIFF]

The rules for sniffing images specifically and the rules for distingushing if a resource is text or binary are also defined in the Content-Type Processing Model specification. Both sets of rules return a MIME type as their result. [MIMESNIFF]

It is imperative that the rules in the Content-Type Processing Model specification be followed exactly. When a user agent uses different heuristics for content type detection than the server expects, security problems can occur. For more details, see the Content-Type Processing Model specification. [MIMESNIFF]

2.7 Common DOM interfaces

2.7.1 Reflecting content attributes in IDL attributes

Some IDL attributes are defined to reflect 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.

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.

If a reflecting IDL attribute is a DOMString attribute whose content attribute is defined to contain a URL, then on getting, the IDL attribute must resolve the value of the content attribute relative to the element and return the resulting absolute URL 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.

If a reflecting IDL attribute is a DOMString attribute whose content attribute is defined to contain one or more URLs, then on getting, the IDL attribute must split the content attribute on spaces and return the concatenation of resolving each token URL to an absolute URL 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.

If a reflecting IDL attribute is a DOMString whose content attribute is an enumerated attribute, and the IDL attribute is limited to only known values, 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, if the new value is an ASCII case-insensitive match for one of the keywords given for that attribute, then the content attribute must be set to the conforming value associated with the state that the attribute would be in if set to the given new value, otherwise, if the new value is the empty string, then the content attribute must be removed, otherwise, the setter must raise a SYNTAX_ERR exception.

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

If a reflecting IDL attribute is a boolean attribute, then on getting the IDL attribute must return true if the 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 have the same value as its name if the IDL attribute is set to true. (This corresponds to the rules for boolean content attributes.)

If a reflecting IDL attribute is a signed integer type (long) then, on getting, the content attribute must be parsed according to the rules for parsing signed integers, 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 valid integer and then that string must be used as the new content attribute value.

If a reflecting IDL attribute is a signed integer type (long) that is limited to only non-negative numbers then, on getting, the content attribute must be parsed according to the rules for parsing non-negative integers, 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 −1 if there is no default value. On setting, if the value is negative, the user agent must fire an INDEX_SIZE_ERR exception. Otherwise, the given value must be converted to the shortest possible string representing the number as a valid non-negative integer and then that string must be used as the new content attribute value.

If a reflecting IDL attribute is an unsigned integer type (unsigned long) then, on getting, the content attribute must be parsed according to the rules for parsing non-negative integers, 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 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 valid non-negative integer and then that string must be used as the new content attribute value.

If a reflecting IDL attribute is an unsigned integer type (unsigned long) that is limited to only non-negative numbers greater than zero, 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 rules for parsing non-negative integers, 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 1 if there is no default value. On setting, if the value is zero, the user agent must fire an INDEX_SIZE_ERR exception. Otherwise, the given value must be converted to the shortest possible string representing the number as a valid non-negative integer and then that string must be used as the new content attribute value.

If a reflecting IDL attribute is a floating point number type (float), then, on getting, the content attribute must be parsed according to the rules for parsing floating point number values, 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 best representation of the number as a floating point number and then that string must be used as the new content attribute value.

The values Infinity and Not-a-Number (NaN) values throw an exception on setting, as defined earlier.

If a reflecting IDL attribute is of the type DOMTokenList or DOMSettableTokenList, then on getting it must return a DOMTokenList or DOMSettableTokenList 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 DOMTokenList or DOMSettableTokenList object must be returned every time for each attribute.

If an element with no attributes has its element.classList.remove() 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 element.classList.add() method is then invoked, a class attribute will be added to the element with the value of the token to be added.

If a reflecting IDL attribute has the type HTMLElement, or an interface that descends from HTMLElement, then, on getting, it must run the following algorithm (stopping at the first point where a value is returned):

  1. If the corresponding content attribute is absent, then the IDL attribute must return null.
  2. Let candidate be the element that the document.getElementById() method would find if it was passed as its argument the current value of the corresponding content attribute.
  3. If candidate is null, or if it is not type-compatible with the IDL attribute, then the IDL attribute must return null.
  4. Otherwise, it must return candidate.

On setting, if the given element has an id attribute, then the content attribute must be set to the value of that id attribute. Otherwise, the IDL attribute must be set to the empty string.

2.7.2 Collections

The HTMLCollection, HTMLAllCollection, HTMLFormControlsCollection, HTMLOptionsCollection, and HTMLPropertiesCollection interfaces represent various lists of DOM nodes. Collectively, objects implementing these interfaces are called collections.

When a collection is created, a filter and a root are associated with the collection.

For example, when the HTMLCollection object for the document.images attribute is created, it is associated with a filter that selects only img elements, and rooted at the root of the document.

The collection then represents a live view of the subtree rooted at the collection's root, containing only nodes that match the given filter. The view is linear. In the absence of specific requirements to the contrary, the nodes within the collection must be sorted in tree order.

The rows list is not in tree order.

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

2.7.2.1 HTMLCollection

The HTMLCollection interface represents a generic collection of elements.

interface HTMLCollection {
  readonly attribute unsigned long length;
  caller getter Element item(in unsigned long index);
  caller getter Element namedItem(in DOMString name);
};
collection . length

Returns the number of elements in the collection.

element = collection . item(index)
collection[index]
collection(index)

Returns the item with index index from the collection. The items are sorted in tree order.

Returns null if index is out of range.

element = collection . namedItem(name)
collection[name]
collection(name)

Returns the first item with ID or name name from the collection.

Returns null if no element with that ID or name could be found.

Only a, applet, area, embed, form, frame, frameset, iframe, img, and object elements can have a name for the purpose of this method; their name is given by the value of their name attribute.

The object's indices of the supported indexed properties are the numbers in the range zero to one less than the number of nodes represented by the collection. If there are no such elements, then there are no supported indexed properties.

The length attribute must return the number of nodes represented by the collection.

The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must return null.

The names of the supported named properties consist of the values of the name attributes of each a, applet, area, embed, form, frame, frameset, iframe, img, and object element represented by the collection with a name attribute, plus the list of IDs that the elements represented by the collection have.

The namedItem(key) method must return the first node in the collection that matches the following requirements:

If no such elements are found, then the method must return null.

2.7.2.2 HTMLAllCollection

The HTMLAllCollection interface represents a generic collection of elements just like HTMLCollection, with the exception that its namedItem() method returns an HTMLCollection object when there are multiple matching elements.

interface HTMLAllCollection : HTMLCollection {
  // inherits length and item()
  caller getter object namedItem(in DOMString name); // overrides inherited namedItem()
  HTMLAllCollection tags(in DOMString tagName);
};
collection . length

Returns the number of elements in the collection.

element = collection . item(index)
collection[index]
collection(index)

Returns the item with index index from the collection. The items are sorted in tree order.

Returns null if index is out of range.

element = collection . namedItem(name)
collection = collection . namedItem(name)
collection[name]
collection(name)

Returns the item with ID or name name from the collection.

If there are multiple matching items, then an HTMLAllCollection object containing all those elements is returned.

Returns null if no element with that ID or name could be found.

Only a, applet, area, embed, form, frame, frameset, iframe, img, and object elements can have a name for the purpose of this method; their name is given by the value of their name attribute.

collection = collection . tags(tagName)

Returns a collection that is a filtered view of the current collection, containing only elements with the given tag name.

The object's indices of the supported indexed properties and names of the supported named properties are as defined for HTMLCollection objects.

The namedItem(key) method must act according to the following algorithm:

  1. Let collection be an HTMLAllCollection object rooted at the same node as the HTMLAllCollection object on which the method was invoked, whose filter matches only only elements that already match the filter of the HTMLAllCollection object on which the method was invoked and that are either:

  2. If, at the time the method is called, there is exactly one node in collection, then return that node and stop the algorithm.
  3. Otherwise, if, at the time the method is called, collection is empty, return null and stop the algorithm.
  4. Otherwise, return collection.

The tags(tagName) method must return an HTMLAllCollection rooted at the same node as the HTMLAllCollection object on which the method was invoked, whose filter matches only HTML elements whose local name is the tagName argument and that already match the filter of the HTMLAllCollection object on which the method was invoked. In HTML documents, the argument must first be converted to ASCII lowercase.

2.7.2.3 HTMLFormControlsCollection

The HTMLFormControlsCollection interface represents a collection of listed elements in form and fieldset elements.

interface HTMLFormControlsCollection : HTMLCollection {
  // inherits length and item()
  caller getter object namedItem(in DOMString name); // overrides inherited namedItem()
};

interface RadioNodeList : NodeList {
          attribute DOMString value;
};
collection . length

Returns the number of elements in the collection.

element = collection . item(index)
collection[index]
collection(index)

Returns the item with index index from the collection. The items are sorted in tree order.

Returns null if index is out of range.

element = collection . namedItem(name)
radioNodeList = collection . namedItem(name)
collection[name]
collection(name)

Returns the item with ID or name name from the collection.

If there are multiple matching items, then a RadioNodeList object containing all those elements is returned.

Returns null if no element with that ID or name could be found.

radioNodeList . value [ = value ]

Returns the value of the first checked radio button represented by the object.

Can be set, to check the first radio button with the given value represented by the object.

The object's indices of the supported indexed properties are as defined for HTMLCollection objects.

The names of the supported named properties consist of the values of all the id and name attributes of all the elements represented by the collection.

The namedItem(name) method must act according to the following algorithm:

  1. If, at the time the method is called, there is exactly one node in the collection that has either an id attribute or a name attribute equal to name, then return that node and stop the algorithm.
  2. Otherwise, if there are no nodes in the collection that have either an id attribute or a name attribute equal to name, then return null and stop the algorithm.
  3. Otherwise, create a RadioNodeList object representing a live view of the HTMLFormControlsCollection object, further filtered so that the only nodes in the RadioNodeList object are those that have either an id attribute or a name attribute equal to name. The nodes in the RadioNodeList object must be sorted in tree order.
  4. Return that RadioNodeList object.

Members of the RadioNodeList interface inherited from the NodeList interface must behave as they would on a NodeList object.

The value IDL attribute on the RadioNodeList object, on getting, must return the value returned by running the following steps:

  1. Let element be the first element in tree order represented by the RadioNodeList object that is an input element whose type attribute is in the Radio Button state and whose checkedness is true. Otherwise, let it be null.

  2. If element is null, or if it is an element with no value attribute, return the empty string.

  3. Otherwise, return the value of element's value attribute.

On setting, the value IDL attribute must run the following steps:

  1. Let element be the first element in tree order represented by the RadioNodeList object that is an input element whose type attribute is in the Radio Button state and whose value content attribute is present and equal to the new value, if any. Otherwise, let it be null.

  2. If element is not null, then set its checkedness to true.

2.7.2.4 HTMLOptionsCollection

The HTMLOptionsCollection interface represents a list of option elements. It is always rooted on a select element and has attributes and methods that manipulate that element's descendants.

interface HTMLOptionsCollection : HTMLCollection {
  // inherits item()
           attribute unsigned long length; // overrides inherited length
  caller getter object namedItem(in DOMString name); // overrides inherited namedItem()
  void add(in HTMLElement element, in optional HTMLElement before);
  void add(in HTMLElement element, in long before);
  void remove(in long index);
};
collection . length [ = value ]

Returns the number of elements in the collection.

When set to a smaller number, truncates the number of option elements in the corresponding container.

When set to a greater number, adds new blank option elements to that container.

element = collection . item(index)
collection[index]
collection(index)

Returns the item with index index from the collection. The items are sorted in tree order.

Returns null if index is out of range.

element = collection . namedItem(name)
nodeList = collection . namedItem(name)
collection[name]
collection(name)

Returns the item with ID or name name from the collection.

If there are multiple matching items, then a NodeList object containing all those elements is returned.

Returns null if no element with that ID could be found.

collection . add(element [, before ] )

Inserts element before the node given by before.

The before argument can be a number, in which case element is inserted before the item with that number, or an element from the collection, in which case element is inserted before that element.

If before is omitted, null, or a number out of range, then element will be added at the end of the list.

This method will throw a HIERARCHY_REQUEST_ERR exception if element is an ancestor of the element into which it is to be inserted. If element is not an option or optgroup element, then the method does nothing.

The object's indices of the supported indexed properties are as defined for HTMLCollection objects.

On getting, the length attribute must return the number of nodes represented by the collection.

On setting, the behavior depends on whether the new value is equal to, greater than, or less than the number of nodes represented by the collection at that time. If the number is the same, then setting the attribute must do nothing. If the new value is greater, then n new option elements with no attributes and no child nodes must be appended to the select element on which the HTMLOptionsCollection is rooted, where n is the difference between the two numbers (new value minus old value). If the new value is lower, then the last n nodes in the collection must be removed from their parent nodes, where n is the difference between the two numbers (old value minus new value).

Setting length never removes or adds any optgroup elements, and never adds new children to existing optgroup elements (though it can remove children from them).

The names of the supported named properties consist of the values of all the id and name attributes of all the elements represented by the collection.

The namedItem(name) method must act according to the following algorithm:

  1. If, at the time the method is called, there is exactly one node in the collection that has either an id attribute or a name attribute equal to name, then return that node and stop the algorithm.
  2. Otherwise, if there are no nodes in the collection that have either an id attribute or a name attribute equal to name, then return null and stop the algorithm.
  3. Otherwise, create a NodeList object representing a live view of the HTMLOptionsCollection object, further filtered so that the only nodes in the NodeList object are those that have either an id attribute or a name attribute equal to name. The nodes in the NodeList object must be sorted in tree order.
  4. Return that NodeList object.

The add(element, before) method must act according to the following algorithm:

  1. If element is not an option or optgroup element, then return and abort these steps.

  2. If element is an ancestor of the select element on which the HTMLOptionsCollection is rooted, then throw a HIERARCHY_REQUEST_ERR exception.

  3. If before is an element, but that element isn't a descendant of the select element on which the HTMLOptionsCollection is rooted, then throw a NOT_FOUND_ERR exception.

  4. If element and before are the same element, then return and abort these steps.

  5. If before is a node, then let reference be that node. Otherwise, if before is an integer, and there is a beforeth node in the collection, let reference be that node. Otherwise, let reference be null.

  6. If reference is not null, let parent be the parent node of reference. Otherwise, let parent be the select element on which the HTMLOptionsCollection is rooted.

  7. Act as if the DOM Core insertBefore() method was invoked on the parent node, with element as the first argument and reference as the second argument.

The remove(index) method must act according to the following algorithm:

  1. If the number of nodes represented by the collection is zero, abort these steps.

  2. If index is not a number greater than or equal to 0 and less than the number of nodes represented by the collection, let element be the first element in the collection. Otherwise, let element be the indexth element in the collection.

  3. Remove element from its parent node.

2.7.2.5 HTMLPropertiesCollection

The HTMLPropertiesCollection interface represents a collection of elements that add name-value pairs to a particular item in the microdata model.

interface HTMLPropertiesCollection : HTMLCollection {
  // inherits length and item()
  caller getter PropertyNodeList namedItem(in DOMString name); // overrides inherited namedItem()
  readonly attribute DOMStringList names;
};

typedef sequence<any> PropertyValueArray;

interface PropertyNodeList : NodeList {
  readonly attribute PropertyValueArray values;
};
collection . length

Returns the number of elements in the collection.

element = collection . item(index)
collection[index]
collection(index)

Returns the element with index index from the collection. The items are sorted in tree order.

Returns null if index is out of range.

propertyNodeList = collection . namedItem(name)
collection[name]
collection(name)

Returns a PropertyNodeList object containing any elements that add a property named name.

collection . names

Returns a DOMStringList with the property names of the elements in the collection.

propertyNodeList . values

Returns an array of the various values that the relevant elements have.

The object's indices of the supported indexed properties are as defined for HTMLCollection objects.

The names of the supported named properties consist of the property names of all the elements represented by the collection.

The names attribute must return a live DOMStringList object giving the property names of all the elements represented by the collection, listed in tree order, but with duplicates removed, leaving only the first occurrence of each name. The same object must be returned each time.

The namedItem(name) method must return a PropertyNodeList object representing a live view of the HTMLPropertiesCollection object, further filtered so that the only nodes in the PropertyNodeList object are those that have a property name equal to name. The nodes in the PropertyNodeList object must be sorted in tree order, and the same object must be returned each time a particular name is queried.


Members of the PropertyNodeList interface inherited from the NodeList interface must behave as they would on a NodeList object.

The values IDL attribute on the PropertyNodeList object, on getting, must return a newly constructed array whose values are the values obtained from the itemValue DOM property of each of the elements represented by the object, in tree order.

2.7.3 DOMTokenList

The DOMTokenList interface represents an interface to an underlying string that consists of a set of space-separated tokens.

DOMTokenList objects are always case-sensitive, even when the underlying string might ordinarily be treated in a case-insensitive manner.

interface DOMTokenList {
  readonly attribute unsigned long length;
  getter DOMString item(in unsigned long index);
  boolean contains(in DOMString token);
  void add(in DOMString token);
  void remove(in DOMString token);
  boolean toggle(in DOMString token);
  stringifier DOMString ();
};
tokenlist . length

Returns the number of tokens in the string.

element = tokenlist . item(index)
tokenlist[index]

Returns the token with index index. The tokens are returned in the order they are found in the underlying string.

Returns null if index is out of range.

hastoken = tokenlist . contains(token)

Returns true if the token is present; false otherwise.

Throws a SYNTAX_ERR exception if token is empty.

Throws an INVALID_CHARACTER_ERR exception if token contains any spaces.

tokenlist . add(token)

Adds token, unless it is already present.

Throws a SYNTAX_ERR exception if token is empty.

Throws an INVALID_CHARACTER_ERR exception if token contains any spaces.

tokenlist . remove(token)

Removes token if it is present.

Throws a SYNTAX_ERR exception if token is empty.

Throws an INVALID_CHARACTER_ERR exception if token contains any spaces.

hastoken = tokenlist . toggle(token)

Adds token if it is not present, or removes it if it is.

Throws a SYNTAX_ERR exception if token is empty.

Throws an INVALID_CHARACTER_ERR exception if token contains any spaces.

The length attribute must return the number of tokens that result from splitting the underlying string on spaces. This is the length.

The object's indices of the supported indexed properties are the numbers in the range zero to length-1, unless the length is zero, in which case there are no supported indexed properties.

The item(index) method must split the underlying string on spaces, preserving the order of the tokens as found in the underlying string, and then return the indexth item in this list. If index is equal to or greater than the number of tokens, then the method must return null.

For example, if the string is "a b a c" then there are four tokens: the token with index 0 is "a", the token with index 1 is "b", the token with index 2 is "a", and the token with index 3 is "c".

The contains(token) method must run the following algorithm:

  1. If the token argument is the empty string, then raise a SYNTAX_ERR exception and stop the algorithm.
  2. If the token argument contains any space characters, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  3. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  4. If the token indicated by token is a case-sensitive match for one of the tokens in the object's underlying string then return true and stop this algorithm.
  5. Otherwise, return false.

The add(token) method must run the following algorithm:

  1. If the token argument is the empty string, then raise a SYNTAX_ERR exception and stop the algorithm.
  2. If the token argument contains any space characters, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  3. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  4. If the given token is a case-sensitive match for one of the tokens in the DOMTokenList object's underlying string then stop the algorithm.
  5. Otherwise, if the DOMTokenList object's underlying string is not the empty string and the last character of that string is not a space character, then append a U+0020 SPACE character to the end of that string.
  6. Append the value of token to the end of the DOMTokenList object's underlying string.

The remove(token) method must run the following algorithm:

  1. If the token argument is the empty string, then raise a SYNTAX_ERR exception and stop the algorithm.
  2. If the token argument contains any space characters, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  3. Otherwise, remove the given token from the underlying string.

The toggle(token) method must run the following algorithm:

  1. If the token argument is the empty string, then raise a SYNTAX_ERR exception and stop the algorithm.
  2. If the token argument contains any space characters, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  3. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  4. If the given token is a case-sensitive match for one of the tokens in the DOMTokenList object's underlying string then remove the given token from the underlying string and stop the algorithm, returning false.
  5. Otherwise, if the DOMTokenList object's underlying string is not the empty string and the last character of that string is not a space character, then append a U+0020 SPACE character to the end of that string.
  6. Append the value of token to the end of the DOMTokenList object's underlying string.
  7. Return true.

Objects implementing the DOMTokenList interface must stringify to the object's underlying string representation.

2.7.4 DOMSettableTokenList

The DOMSettableTokenList interface is the same as the DOMTokenList interface, except that it allows the underlying string to be directly changed.

interface DOMSettableTokenList : DOMTokenList {
            attribute DOMString value;
};
tokenlist . value

Returns the underlying string.

Can be set, to change the underlying string.

An object implementing the DOMSettableTokenList interface must act as defined for the DOMTokenList interface, except for the value attribute defined here.

The value attribute must return the underlying string on getting, and must replace the underlying string with the new value on setting.

2.7.5 Safe passing of structured data

When a user agent is required to obtain a structured clone of an object, it must run the following algorithm, which either returns a separate object, or throws an exception.

  1. Let input be the object being cloned.

  2. Let memory be a list of objects, initially empty. (This is used to catch cycles.)

  3. Let output be the object resulting from calling the internal structured cloning algorithm with input and memory.

  4. Return output.

The internal structured cloning algorithm is always called with two arguments, input and memory, and its behavior depends on the type of input, as follows:

If input is the undefined value

Return the undefined value.

If input is the null value

Return the null value.

If input is the false value

Return the false value.

If input is the true value

Return the true value.

If input is a Number object

Return a newly constructed Number object with the same value as input.

If input is a String object

Return a newly constructed String object with the same value as input.

If input is a Date object

Return a newly constructed Date object with the same value as input.

If input is a RegExp object

Return a newly constructed RegExp object with the same pattern and flags as input.

The value of the lastIndex property is not copied.

If input is a ImageData object

Return a newly constructed ImageData object with the same width and height as input, and with a newly constructed CanvasPixelArray for its data attribute, with the same length and pixel values as the input's.

If input is a File object

Return a newly constructed File object corresponding to the same underlying data.

If input is a Blob object

Return a newly constructed Blob object corresponding to the same underlying data.

If input is a FileList object

Return a newly constructed FileList object containing a list of newly constructed File objects corresponding to the same underlying data as those in input, maintaining their relative order.

If input is a host object (e.g. a DOM node)

Return the null value.

If input is an Array object
If input is an Object object
  1. If input is in memory, then throw a NOT_SUPPORTED_ERR exception and abort the overall structured clone algorithm.

  2. Otherwise, let new memory be a list consisting of the items in memory with the addition of input.

  3. Create a new object, output, of the same type as input: either an Array or an Object.

  4. For each enumerable property in input, add a corresponding property to output having the same name, and having a value created from invoking the internal structured cloning algorithm recursively with the value of the property as the "input" argument and new memory as the "memory" argument. The order of the properties in the input and output objects must be the same.

    This does not walk the prototype chain.

  5. Return output.

If input is another native object type (e.g. Error)

Return the null value.

2.7.6 DOMStringMap

The DOMStringMap interface represents a set of name-value pairs. It exposes these using the scripting language's native mechanisms for property access.

When a DOMStringMap 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.

interface DOMStringMap {
  getter DOMString (in DOMString name);
  setter void (in DOMString name, in DOMString value);
  creator void (in DOMString name, in DOMString value);
  deleter void (in DOMString name);
};

The names of the supported named properties on a DOMStringMap 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.

When a DOMStringMap object is indexed to retrieve a named property name, the value returned must be the value component of the name-value pair whose name component is name in the list returned by the algorithm for getting the list of name-value pairs.

When a DOMStringMap object is indexed to create or modify a named property name with value value, the algorithm for setting names to certain values must be run, passing name as the name and the result of converting value to a DOMString as the value.

When a DOMStringMap object is indexed to delete a named property named name, the algorithm for deleting names must be run, passing name as the name.

The DOMStringMap interface definition here is only intended for JavaScript environments. Other language bindings will need to define how DOMStringMap is to be implemented for those languages.

The dataset attribute on elements exposes the data-* attributes on the element.

Given the following fragment and elements with similar constructions:

<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">

...one could imagine a function splashDamage() that takes some arguments, the first of which is the element to process:

function splashDamage(node, x, y, damage) {
  if (node.classList.contains('tower') && // checking the 'class' attribute
      node.dataset.x == x && // 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 < 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
  }
}

2.7.7 DOM feature strings

DOM3 Core defines mechanisms for checking for interface support, and for obtaining implementations of interfaces, using feature strings. [DOMCORE]

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.

For historical reasons, user agents should return the true value when the hasFeature(feature, version) method of the DOMImplementation interface is invoked with feature set to either "HTML" or "XHTML" and version set to either "1.0" or "2.0".

2.7.8 Exceptions

The following are DOMException codes. [DOMCORE]

  1. INDEX_SIZE_ERR
  2. DOMSTRING_SIZE_ERR
  3. HIERARCHY_REQUEST_ERR
  4. WRONG_DOCUMENT_ERR
  5. INVALID_CHARACTER_ERR
  6. NO_DATA_ALLOWED_ERR
  7. NO_MODIFICATION_ALLOWED_ERR
  8. NOT_FOUND_ERR
  9. NOT_SUPPORTED_ERR
  10. INUSE_ATTRIBUTE_ERR
  11. INVALID_STATE_ERR
  12. SYNTAX_ERR
  13. INVALID_MODIFICATION_ERR
  14. NAMESPACE_ERR
  15. INVALID_ACCESS_ERR
  16. VALIDATION_ERR
  17. TYPE_MISMATCH_ERR
  18. SECURITY_ERR
  19. NETWORK_ERR
  20. ABORT_ERR
  21. URL_MISMATCH_ERR
  22. QUOTA_EXCEEDED_ERR
  23. PARSE_ERR
  24. SERIALIZE_ERR

2.7.9 Garbage collection

There is an implied strong reference from any IDL attribute that returns a pre-existing object to that object.

For example, the document.location attribute means that there is a strong reference from a Document object to its Location object. Similarly, there is always a strong reference from a Document to any descendant nodes, and from any node to its owner Document.