Please refer to the errata for this document, which may include some normative corrections.
See also translations.
Copyright © 2013 W3C® (MIT, ERCIM, Keio, Beihang), All Rights Reserved. W3C liability, trademark and document use rules apply.
This specification defines an application programming interface (API) for widgets that provides, amongst other things, functionality for accessing a widget's metadata and persistently storing data.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.
This document has been reviewed by W3C Members, by software developers, and by other W3C groups and interested parties, and is endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited from another document. W3C's role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.
This is the 31 October 2013 W3C Recommendation of the Widget Interface specification. The Last Call period for this specification ended on 28 June 2011. As the implementation report shows, the exit criteria for the Candidate Recommendation phase was met (at least two conforming implementations pass the test suite).
By publishing this Recommendation, W3C expects that the functionality specified in this Widget Interface API will not be affected by changes to HTML5 or WebIDL as that specification proceeds to Recommendation.
This document is produced by the Web Applications WG, part of the Rich Web Client Activity in the W3C Interaction Domain. It is expected that this document will progress along the W3C's Recommendation track. The public is encouraged to send comments to the WebApps Working Group's public mailing list public-webapps@w3.org (archive) by the 15 February 2012. See W3C mailing list and archive usage guidelines. Advisory Committee Representatives should consult their questionnaires.
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WindowWidget
Interface
Widget
Interface
WidgetStorage
Interface
This section is non-normative.
This specification defines an application programming interface that enables the ability to:
This section is non-normative.
This specification is part of the Widgets family of specifications, which together standardize widgets as a whole. The list of specifications that make up the Widgets family of specifications can be found on the Web Applications Working Group's wiki.
This section is non-normative.
The design goals for this specification are documented in the [Widget Requirements] document. This document addresses some of the requirements relating to Application Programming Interfaces of the [Widget Requirements] document:
Instantiated Widget API: addressed by widget
object.
IDL Definitions: to meet this requirement, this specification makes use of [WebIDL].
Manipulation of Author-defined start-up values: addressed by
using a widget storage area and
preferences
attribute's extension of the
Storage
interface defined in [Web
Storage].
Configuration Document Data: this is addressed by the
widget
object's attributes.
All examples and notes in this specification are non-normative, as are all sections explicitly marked as non-normative. Everything else in this specification is normative.
The key words must, must not, should, recommended, may and optional in the normative parts of this specification are to be interpreted as described in [RFC2119].
The IDL blocks in this specification are conforming IDL fragments as defined by the WebIDL specification.
Only user agents can claim conformance to this specification. Conformance requirements phrased as algorithms or specific steps can be implemented in any manner, so long as the end result is equivalent to what would be achieved when following the specification.
Note: Implementations can partially check their level of conformance to this specification by successfully passing the test cases of the [Interface-Test-Suite]. Passing all the tests in the test suite does not imply conformance to this specification; It only implies that the implementation conforms to aspects tested by the test suite.
The following definitions are used throughout this specification. Please note that the following list is not exhaustive; other terms are defined throughout this specification.
Some code running within a widget instance (e.g., some ECMAScript).
A configuration document is reserved file called
"config.xml
" at the root of the widget package as
specified in the [Widgets-Packaging] specification.
A DOM attribute is said to be getting when its value is being retrieved (e.g. by an author script).
The act of user agent processing a widget package through the Steps for Processing a Widget Package, as specified in the [Widgets-Packaging] specification.
A persistently stored name-value pair that is associated with the widget the first time the widget is initiated.
A file in the widget package to be loaded by the user agent when it instantiates the widget, as specified in the [Widgets-Packaging] specification.
A DOM attribute is said to be setting when its value is being set to some value (e.g. by an author script).
A user agent implements a mentioned specification or conformance clause.
A CSS viewport. For a start file
rendered on
continuous media, as defined in the [CSS]
specification, a viewport is the area on which the
Document
of the start file is rendered by
the user agent. The dimensions of a viewport excludes scrollbars,
toolbars, and other user interface "chrome".
A browsing context that comes into existence after initialization. The concept of a browsing context is defined in [HTML]. Multiple widget instances can be instantiated from a single widget package. A widget instance is unique and does not share any DOM attribute values, widget storage area, or [Web Storage] storage areas with any other widget instance.
A user agent is a software implementation of this specification that also supports the [Widgets-Packaging] specification.
Note: The user agent described in this specification does not denote a "widget user agent" at large. That is, a user agent that implements all the specifications, and dependencies, defined in the widgets family of specifications. The user agent described in this specification is only concerned with the behavior of programming interfaces. A user agent needs to impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial of service attacks, to guard against running out of memory, or to work around platform-specific limitations.
WindowWidget
Interface
For a widget instance, a user
agent must expose a unique object that
implements the Widget
interface to author scripts that are same origin
as the instance of the widget (e.g., a Document
loaded in
a [HTML] iframe
element with content from
within a widget package). User agent implementing [HTML]'s
Window
interface must implement the
Widget
interface as the widget
attribute of
the window
object in the manner defined by the
WindowWidget
interface.
[NoInterfaceObject] interface WindowWidget { readonly attribute Widget widget; }; Window implements WindowWidget;
Widget
Interface
An object that implements the Widget
interface exposes the
following attributes:
interface Widget { readonly attribute DOMString author; readonly attribute DOMString description; readonly attribute DOMString name; readonly attribute DOMString shortName; readonly attribute DOMString version; readonly attribute DOMString id; readonly attribute DOMString authorEmail; readonly attribute DOMString authorHref; readonly attribute WidgetStorage preferences; readonly attribute unsigned long height; readonly attribute unsigned long width; };
Note: A user agent can support the
Storage
interface on DOM attributes other than the
preferences
attribute (e.g., a user agent can support the
[Web Storage] specification's localStorage
attribute of the window
object in conjunction to the
preferences
attribute). For the sake of interoperability
across widget user agents, and where it makes sense, authors can use
the preferences
attribute in conjunction to other APIs
that expose an object that implements the Storage
interface.
If a user agent has previously associated a widget storage
area with a widget instance, the user agent must
not re-create the preferences
attribute unless
explicitly requested to do so by the end-user or for security or
privacy reasons (e.g., the end-user wants to purge personal data).
Instead, the previously associated widget storage area (or
an equivalent clone) can be accessed using the Storage
interface. When an object implementing the Widget
interface is instantiated, if a user agent has not previously
associated a widget storage area with the instance of a widget, then the user agent must create
the preferences
attribute.
This section is non-normative.
This example shows how a widget's metadata can be accessed by through the widget interface.
Given the following configuration document:
<widget xmlns = "http://www.w3.org/ns/widgets" id = "http://example.org/exampleWidget" version = "2.0 Beta" height = "200" width = "200" viewmodes = "floating"> <name short="Example 2.0">The example Widget!</name> <description>A sample widget to demonstrate some of the possibilities.</description> <author href = "http://foo-bar.example.org/" email = "foo-bar@example.org">Foo Bar Corp</author> <preference name = "apikey" value = "ea31ad3a23fd2f" readonly = "true"/> </widget>
And given the following start file:
<!doctype html> <title>About this Widget</title> <style> html { padding: 20px; } #aboutBox{ padding: 20px; box-shadow: 2px 2px 10px #444; border-radius: 15px; background-color: #ECEDCF; text-align:center; } </style> <body onload="makeAboutBox()"> <div id="aboutBox"> <h1><a id="storeLink"><img src="icon.png" id="icon"></a></h1> <h1 id="name">Name</h1> <p id="version">Version: </p> <hr> <p id="description">...</p> <hr> <p id="author">© </p> </div> <script> // example that generates an about box // using metadata from a widget's configuration document. function makeAboutBox(){ var storeLink = document.getElementById("storeLink"); storeLink = storeLink.setAttribute("href", widget.id); var icon = document.getElementById("icon"); icon.setAttribute("alt", widget.shortName); var title = document.getElementById("name"); title.innerHTML = widget.name; var version = document.getElementById("version"); var prodKey = widget.preferences["productKey"]; version.innerHTML += widget.version + " (" + prodKey + ")"; var description = document.getElementById("description"); description.innerHTML = widget.description; var author = document.getElementById("author"); author.innerHTML += widget.author; } </script>
The widget would render as:
Most of the attributes of the widget
interface correspond
to the metadata derived from the initialization process.
When an object implementing the Widget
interface is
instantiated, a user agent sets the
attributes identified in the left column of the configuration
attributes table to the values that correspond to values in
table
of configuration defaults as defined in
[Widgets-Packaging] (identified by the values in the right
hand column).
Attributes | Values in Table of Configuration Defaults | Is localizable string |
---|---|---|
author
|
author name | yes |
version
|
widget version | yes |
shortName
|
widget short name | yes |
name
|
widget name | yes |
description
|
widget description | yes |
authorEmail
|
author email | no |
authorHref
|
author href | no |
id
|
widget id | no |
Upon getting any of the attributes from the attributes column of the configuration attributes table, a user agent must return the corresponding value from the 'Values in Table of Configuration Defaults' column.
Attributes that contain a localizable string are identified by having word yes in the "Is localizable string" column in the Configuration Attributes Table above.
Some attributes in the Configuration Attributes Table come in the form of a localizable string, which is defined by the [Widgets-Packaging] specification as a...
data structure containing a sequence of one or more strings, each having some associated directional information and language information (if any). The purpose of a localizable string is to assist user agent in correctly applying the Unicode [BIDI] algorithm when displaying text.
When getting an attribute that is identified as a localizable string, the user agent must apply the rule for getting localizable strings and return the result.
This example shows how a user agent is expected to behave when an empty configuration document is given:
<widget xmlns = "http://www.w3.org/ns/widgets"/>
Would result in the following being reflected in the through the
widget
object:
<!doctype html> <script> alert(widget.version === "") //true alert(widget.name === "") //true alert(widget.author === "") //true alert(widget.authorEmail === "") //true alert(widget.authorHref === "") //true alert(widget.description === "") //true alert(widget.id === "") //true alert(widget.shortName === "") //true </script>
width
Attribute
Upon getting the width
attribute, a
user agent must
return a number that represents the width of the widget instance’s viewport in
[CSS] pixels.
height
Attribute
Upon getting the height
attribute, a
user agent must
return a number that represents the height of the widget instance’s viewport in
[CSS] pixels.
preferences
Attribute
The preferences
attribute allows authors to manipulate a
widget storage area that is unique for the instance of a widget. It does this by
implementing the Storage
interface specified in [Web
Storage].
Upon invocation of the setItem()
,
removeItem()
and clear()
methods, if the
invocation did something, a user agent
must dispatch a storage event
akin to what is specified in "the storage
event" section of [Web Storage] (i.e., the
preferences
attribute behaves the same as
localStorage
with regards to dispatching events).
Upon invocation of the setItem()
or
removeItem()
method by an author script on a
read-only item, a user
agent must throw a
NO_MODIFICATION_ALLOWED_ERR
exception and must not fire a storage event. The
NO_MODIFICATION_ALLOWED_ERR
is defined in the
[DOM3Core] specification.
Upon invocation of the preferences
attribute's
clear()
method, a user
agent must not remove read-only items and corresponding values from a
widget storage area. A user agent must, however, remove other items from the widget
storage area in the manner described in the [Web
Storage] specification without throwing a
NO_MODIFICATION_ALLOWED_ERR
exception for items that the
user agent cannot remove.
When getting or setting the
preferences
attribute, if the origin of a
widget instance is mutable (e.g., if the user agent allows
document.domain
to be dynamically changed), then the
user agent must
perform the preference-origin security check. The concept
of origin is defined in [HTML].
The steps to perform the preference-origin security check are given by the following algorithm:
The user agent may throw a
SECURITY_ERR
exception instead of returning a
Storage
object if the request violates a policy
decision (e.g. if the user agent is configured to not allow the
page to persist data).
If the Document
's origin is not a
scheme/host/port tuple, then throw a SECURITY_ERR
exception and abort these steps.
Otherwise, return the Storage
object associated with
that widget instance's
preferences
attribute.
preferences
Attribute
The steps to create the preferences
attribute
are given by the following algorithm:
Create a widget storage area that is unique for the origin of this instance of a widget.
If the widget preferences variable of the table of configuration defaults contains any preferences, then for each preference held by widget preferences:
Let pref-key be the name of the preference.
If the pref-key already exists in the storage area, stop processing this preference: go back to step 2 in this algorithm, and process the next preference (if any).
Let pref-value be the value of the preference.
Add pref-key and pref-value to the widget storage area:
If the user agent cannot write to the widget storage area (e.g., because it ran out of disk space, or the space quota was exceeded, etc.), terminate all processing of this widget. It is recommended that the user agent inform the end-user of the error.
If this preference's associated
readonly value is true
, then flag
this key as a read-only item in the
widget storage area.
Implement the Storage interface on the widget
storage area, and make the preferences
attribute a pointer to that storage area.
This section is non-normative.
The following example shows the different means by which an author can
interface with the widget
object's
preferences
attribute in ECMAScript. The possibilities
include using either the getItem()
and
setItem()
methods, or bracket access (or a combination of
both).
<!doctype html> ... <fieldset id="prefs-form"> <legend>Game Options</legend> <label>Volume: <input type="range" min="0" max="100" name="volume"/> </label> <label>Difficulty: <input type="range" min="0" max="100" name="difficulty"/> </label> <input type="button" value="Save" onclick="savePrefs()"/> <input type="button" value="load" onclick="loadPrefs()"/> </fieldset> ... <script> var form = document.getElementById("prefs-form"); var fields = form.querySelectorAll("input[type='range']"); function loadPrefs () { for(var i = 0; i < fields.length; i++){ var field = fields[i]; if (typeof widget.preferences[field.name] !== "undefined") { field.value = widget.preferences.getItem(field.name); } } } function savePrefs () { for(var i = 0; i < fields.length; i++){ var field = fields[i]; widget.preferences.setItem(field.name,field.value); } } </script>
This section is non-normative.
This example demonstrates the expected behavior of a user agent that is interacting with preferences that were declared in a configuration document. The user is able to modify and save various preferences. However, if the user attempts to modify and save the license key, which is set to read-only, the widget will throw an error and display an alert message.
<!-- Configuration Document --> <widget xmlns="http://www.w3.org/ns/widgets"> <name>The 80's: Greatest Hits!</name> <preference name="licenseKey" value="f199bb20-1499-11df" readonly="true"/> <preference name="favtrack" value="billy"/> <preference name="playorder" value="1" /> </widget>
<!doctype html> ... <script> var fields; function init(){ fields = document.forms[0].elements; loadPrefs() } function loadPrefs () { for(var i = 0; i < fields.length; i++){ var field = fields[i]; if (typeof widget.preferences[field.name] !== "undefined") { field.value = widget.preferences[field.name]; } } } function savePrefs () { for(var i = 0; i < fields.length; i++){ var field = fields[i]; try{ widget.preferences.setItem(field.name,field.value); }catch(e){ if(e.code === DOMException.NO_MODIFICATION_ALLOWED_ERR){ alert(e); } } } } </script> <body onload="init()"> <fieldset id="prefs-form"> <legend>Album Playback Settings</legend> <form> <label>Volume: <input type="range" min="0" max="100" step="10.0" value="50" name="volume"> </label> <label>Playback: <select name="playorder"> <option value=0>Loop <option value=1>Random <option value=2>Normal </select> </label> <label>Favorite Song <select name="favtrack"> <option value=kate>Kate Bush: Babooshka <option value=billy>Billy Idol: White Wedding <option value=culture>Culture Club: Karma Chameleon </select> </label> <label>License Key: <input name="licenseKey"></label> </form> <button onclick="savePrefs()">Save</button> <button onclick="loadPrefs()">Load</button> </fieldset> ...
WidgetStorage
Interface
The WidgetStorage
Interface extends [Web
Storage]'s Storage
interface so that it can provide
the necessary functionality provided by this specification. It does not
add any new methods or attributes; it just provides a wrapper that
makes it easier to implement on some platforms.
[NoInterfaceObject] interface WidgetStorage : Storage { };
This example shows how to work out if a storage event
came from the widget or from the Web Storage's
localStorage
.
<!doctype html> <script> //note that this code is only really useful inside an iframe! window.addEventListener("storage", function handleStorage(event){ if (event.storageArea === widget.preferences) { //the event was fired by the widget } else if (event.storageArea === window.localStorage || event.storageArea === window.sessionStorage){ //the event was fired by the Web Storage } else { //the event was fired by some other object. } }); </script>
A widget storage area is a data-store that is unique for the
widget instance that uses [Web Storage]'s
Storage
interface but modifies the behavior of [Web
Storage] by allowing some items to be read-only. A user agent uses a widget
storage area to store key-value pairs that pertain to the
preferences
attribute. An author script
interfaces with the widget storage area via the [Web
Storage] specification's Storage
interface.
A user agent must preserve the values stored in a widget storage area when a widget is re-instantiated (i.e., when the device is rebooted and the widget is reopened, the previously set data is made available to the widget storage area).
As an extension to the [Web Storage] specification, a
widget storage area allows certain key-value pairs (items)
to be read-only: a read-only item is an item in a
widget storage area that cannot be modified or deleted by
an author script. A read-only item
always represents a preference that author explicitly
flagged as "read-only" in the widget's configuration
document (denoted by a preference
element
having a readonly
attribute value set to
true
).
The rule for getting localizable strings is as follows:
Let lString be a copy of the localizable string to be processed.
If lString has no directional information associated
with it (i.e., no dir
attribute was used anywhere in
the ancestor chain of the element or attribute in question), and
the localized string does not contain any sub-strings with
directional information within the string itself, return the
lString and terminate this algorithm.
For example, the consider the following configuration document :
<widget xmlns = "http://www.w3.org/ns/widgets" version = "1.0"> <name>Hello</name> </widget>
Would result in the following in the API:
<!doctype html> <script> alert(widget.version === "1.0") //returns true alert(widget.name === "Hello") //returns true </script>
If the lString contains directional information and/or contains any sub-strings with directional information, then recursively do the following from the outermost string to the inner most sub-string of lString:
Let direction be the direction of the sub-string.
lro
ltr
rlo
rtl
Append the sub-string with a U+202C 'POP DIRECTIONAL FORMATTING' character.
Return lString.
This section is non-normative.
The following configuration document demonstrates how having an
dir
attribute is handled by the Widget API:
<widget xmlns = "http://www.w3.org/ns/widgets" version = "1.0" dir = "ltr"> <name>Hello</name> </widget>
Would result in the following in the API:
<!doctype html> <title>Example 1</title> <body style="background-color: #ECEDCF"> <p id ="name"></p> <p id = "version"> </p> <script> var nameElem = document.getElementById("name"); var versionElem = document.getElementById("version"); nameElem.innerHTML = 'The widget's name is "' + widget.name + '". <br>Escaped, the value of name is "' + escape(widget.name) + '".'; versionElem.innerHTML = 'The widget\'s version is "' + widget.version + '". <br> Escaped, the value of version is "' + escape(widget.version) +'".'; </script>
Would render as:
This section is non-normative.
Given this configuration document, where the widget element has
dir
set to ltr
and name has a
span
element with a dir
attribute set to
lro
:
<widget xmlns = "http://www.w3.org/ns/widgets" version = "1.0" dir = "ltr"> <name><span dir="rlo">olleH</span></name> </widget>
The following would result in the start file of the widget:
<!doctype html> <title>Example 2</title> <body style="background-color: #ECEDCF"> <p id ="name"></p> <p id = "version"> </p> <script> var nameElem = document.getElementById("name"); var versionElem = document.getElementById("version"); nameElem.innerHTML = 'The widget\'s name is "' + widget.name + '". <br>Escaped, the value of name is "' + escape(widget.name) + '".'; versionElem.innerHTML = 'The widget\'s version is "' + widget.version + '". <br> Escaped, the value of version is "' + escape(widget.version) +'".'; </script>
Would render as:
This section is non-normative.
Given this configuration document, where the widget element has no
base direction set, the name
has two span
element with a dir
attribute set to lro
:
<widget xmlns = "http://www.w3.org/ns/widgets" version = "1.0"> <name> Hello1 <span dir="rlo">2olleH</span> Goodbye1 <span dir="rlo">2eybdooG</span> </name> </widget>
The following would result in the start file of the widget:
<!doctype html> <title>Example 3</title> <body style="background-color: #ECEDCF"> <p id ="name"></p> <p id = "version"> </p> <script> var nameElem = document.getElementById("name"); var versionElem = document.getElementById("version"); nameElem.innerHTML = 'The widget\'s name is "' + widget.name + '". <br>Escaped, the value of name is "' + escape(widget.name) + '".'; versionElem.innerHTML = 'The widget\'s version is "' + widget.version + '". <br> Escaped, the value of version is "' + escape(widget.version) +'".'; </script>
Would render as:
Clarified "the origin of a widget instance" based on feeback we received that indicated it was unclear.
Added example of how to compare storage areas.
Added WidgetStorage
interface.
Clarified storage event text (hopefully).
Editorial cleanup, found a few conformance requirements that were not being tested.
Removed the definition of valid IRI, as it was not referenced anywhere.
Removed the definition of feature, as it was not referenced anywhere.
Added examples for i18n related material.
The 7 September, 2010 version of the specification drops support for
the openURL
method, which was part of previous versions of
this specification. The Working Group found a number of privacy and
security issues relating to openURL
, as well as a way to
achieve the same intended functionality via other means, and hence
decided to drop it from the specification.
The working group recommends that authors use HTML's
a
element to achieve the same functionality, or use the
window.open()
method where appropriate. Some examples of
how the a element can be used to achieve the same functionality as
openURL
are given below. Of course, the examples will only
work on implementations that actually have scheme handlers to handle
each type of URI.
openURL("mailto:jsmith@example.org?subject=A%20Hello&body=hi")
<a
href="mailto:jsmith@example.org?subject=A%20Hello&body=hi">Email
Jane</a>
openURL("tel:+1234567678")
<a href="tel:+1234567678">Call
Bill!</a>
openURL("http://example.org")
<a
href="http://example.org">Example</a>
openURL("sms:+41796431851,+4116321035;?body=hello%20there")
<a
href="sms:+41796431851,+4116321035;?body=hello%20there">SMS
Bob</a>