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A systematic approach to making Web Applications accessible
22 février 2012, par silviaWith the latest developments in HTML5 and the still fairly new ARIA (Accessible Rich Interface Applications) attributes introduced by the W3C WAI (Web Accessibility Initiative), browsers have now implemented many features that allow you to make your JavaScript-heavy Web applications accessible.
Since I began working on making a complex web application accessible just over a year ago, I discovered that there was no step-by-step guide to approaching the changes necessary for creating an accessible Web application. Therefore, many people believe that it is still hard, if not impossible, to make Web applications accessible. In fact, it can be approached systematically, as this article will describe.
This post is based on a talk that Alice Boxhall and I gave at the recent Linux.conf.au titled “Developing accessible Web apps – how hard can it be ?” (slides, video), which in turn was based on a Google Developer Day talk by Rachel Shearer (slides).
These talks, and this article, introduce a process that you can follow to make your Web applications accessible : each step will take you closer to having an application that can be accessed using a keyboard alone, and by users of screenreaders and other accessibility technology (AT).
The recommendations here only roughly conform to the requirements of WCAG (Web Content Accessibility Guidelines), which is the basis of legal accessibility requirements in many jurisdictions. The steps in this article may or may not be sufficient to meet a legal requirement. It is focused on the practical outcome of ensuring users with disabilities can use your Web application.
Step-by-step Approach
The steps to follow to make your Web apps accessible are as follows :
- Use native HTML tags wherever possible
- Make interactive elements keyboard accessible
- Provide extra markup for AT (accessibility technology)
If you are a total newcomer to accessibility, I highly recommend installing a screenreader and just trying to read/navigate some Web pages. On Windows you can install the free NVDA screenreader, on Mac you can activate the pre-installed VoiceOver screenreader, on Linux you can use Orca, and if you just want a browser plugin for Chrome try installing ChromeVox.
1. Use native HTML tags
As you implement your Web application with interactive controls, try to use as many native HTML tags as possible.
HTML5 provides a rich set of elements which can be used to both add functionality and provide semantic context to your page. HTML4 already included many useful interactive controls, like <a>, <button>, <input> and <select>, and semantic landmark elements like <h1>. HTML5 adds richer <input> controls, and a more sophisticated set of semantic markup elements like such as <time>, <progress>, <meter>, <nav>, <header>, <article> and <aside>. (Note : check browser support for browser support of the new tags).
Using as much of the rich HTML5 markup as possible means that you get all of the accessibility features which have been implemented in the browser for those elements, such as keyboard support, short-cut keys and accessibility metadata, for free. For generic tags you have to implement them completely from scratch.
What exactly do you miss out on when you use a generic tag such as <div> over a specific semantic one such as <button> ?
- Generic tags are not focusable. That means you cannot reach them through using the [tab] on the keyboard.
- You cannot activate them with the space bar or enter key or perform any other keyboard interaction that would be regarded as typical with such a control.
- Since the role that the control represents is not specified in code but is only exposed through your custom visual styling, screenreaders cannot express to their users what type of control it is, e.g. button or link.
- Neither can screenreaders add the control to the list of controls on the page that are of a certain type, e.g. to navigate to all headers of a certain level on the page.
- And finally you need to manually style the element in order for it to look distinctive compared to other elements on the page ; using a default control will allow the browser to provide the default style for the platform, which you can still override using CSS if you want.
Example :
Compare these two buttons. The first one is implemented using a <div> tag, the second one using a <button> tag. Try using a screenreader to experience the difference.
<style> .custombutton cursor : pointer ; border : 1px solid #000 ; background-color : #F6F6F6 ; display : inline-block ; padding : 2px 5px ; </style> <div class="custombutton" onclick="alert(’sent !’)"> Send </div>
<button onclick="alert(’sent !’)"> Send </button>
2. Make interactive elements keyboard accessible
Many sophisticated web applications have some interactive controls that just have no appropriate HTML tag equivalent. In this case, you will have had to build an interactive element with JavaScript and <div> and/or <span> tags and lots of custom styling. The good news is, it’s possible to make even these custom controls accessible, and as a side benefit you will also make your application smoother to use for power users.
The first thing you can do to test usability of your control, or your Web app, is to unplug the mouse and try to use only the [TAB] and [ENTER] keys to interact with your application.
Try the following :
- Can you reach all interactive elements with [TAB] ?
- Can you activate interactive elements with [ENTER] (or [SPACE]) ?
- Are the elements in the right tab order ?
- After interaction : is the right element in focus ?
- Is there a keyboard shortcut that activates the element (accesskey) ?
No ? Let’s fix it.
2.1. Reaching interactive elements
If you have an element on your page that cannot be reached with [TAB], put a @tabindex attribute on it.
Example :
Here we have a <span> tag that works as a link (don’t do this – it’s just a simple example). The first one cannot be reached using [TAB] but the second one has a tabindex and is thus part of the tab order of the HTML page.
(Note : since we experiment lots with the tabindex in this article, to avoid confusion, click on some text in this paragraph and then hit the [TAB] key to see where it goes next. The click will set your keyboard focus in the DOM.)
Click
<style> .customlink text-decoration : underline ; cursor : pointer ; </style> <span class="customlink" onclick="alert(’activated !’)"> Click </span>
Click <style> .customlink text-decoration : underline ; cursor : pointer ; </style> <span class="customlink" onclick="alert(’activated !’)" tabindex="0"> Click </span>
You set @tabindex=0 to add an element into the native tab order of the page, which is the DOM order.
2.2. Activating interactive elements
Next, you typically want to be able to use the [ENTER] and [SPACE] keys to activate your custom control. To do so, you will need to implement an onkeydown event handler. Note that the keyCode for [ENTER] is 13 and for [SPACE] is 32.
Example :
Let’s add this functionality to the <span> tag from before. Try tabbing to it and hit the [ENTER] or [SPACE] key.
Click <span class="customlink" onclick="alert(’activated !’)" tabindex="0"> Click </span>
<script><br />
function handlekey(event) {<br />
var target = event.target || event.srcElement;<br />
if (event.keyCode == 13 || event.keyCode == 32) { target.onclick(); }<br />
}<br />
</script>
Click<span class="customlink" onclick="alert(’activated !’)" tabindex="0" onkeydown="handlekey(event) ;"> Click </span> <script> function handlekey(event) var target = event.target || event.srcElement ; if (event.keyCode == 13 || event.keyCode == 32) target.onclick() ; </script>
Note that there are some controls that might need support for keys other than [tab] or [enter] to be able to use them from the keyboard alone, for example a custom list box, menu or slider should respond to arrow keys.
2.3. Elements in the right tab order
Have you tried tabbing to all the elements on your page that you care about ? If so, check if the order of tab stops seems right. The default order is given by the order in which interactive elements appear in the DOM. For example, if your page’s code has a right column that is coded before the main article, then the links in the right column will receive tab focus first before the links in the main article.
You could change this by re-ordering your DOM, but oftentimes this is not possible. So, instead give the elements that should be the first ones to receive tab focus a positive @tabindex. The tab access will start at the smallest non-zero @tabindex value. If multiple elements share the same @tabindex value, these controls receive tab focus in DOM order. After that, interactive elements and those with @tabindex=0 will receive tab focus in DOM order.
Example :
The one thing that always annoys me the most is if the tab order in forms that I am supposed to fill in is illogical. Here is an example where the first and last name are separated by the address because they are in a table. We could fix it by moving to a <div> based layout, but let’s use @tabindex to demonstrate the change.
Firstname :
Address :
Lastname :
City :
<table class="customtabs"> <tr> <td>Firstname : <input type="text" id="firstname"> </td> <td>Address : <input type="text" id="address"> </td> </tr> <tr> <td>Lastname : <input type="text" id="lastname"> </td> <td>City : <input type="text" id="city"> </td> </tr> </table>
Click here to test this form,
then [TAB] :Firstname :
Address :
Lastname :
City :
<table class="customtabs"> <tr> <td>Firstname : <input type="text" id="firstname" tabindex="10"> </td> <td>Address : <input type="text" id="address" tabindex="30"> </td> </tr> <tr> <td>Lastname : <input type="text" id="lastname" tabindex="20"> </td> <td>City : <input type="text" id="city" tabindex="40"> </td> </tr> </table>
Be very careful with using non-zero tabindex values. Since they change the tab order on the page, you may get side effects that you might not have intended, such as having to give other elements on the page a non-zero tabindex value to avoid skipping too many other elements as I would need to do here.
2.4. Focus on the right element
Some of the controls that you create may be rather complex and open elements on the page that were previously hidden. This is particularly the case for drop-downs, pop-ups, and menus in general. Oftentimes the hidden element is not defined in the DOM right after the interactive control, such that a [TAB] will not put your keyboard focus on the next element that you are interacting with.
The solution is to manage your keyboard focus from JavaScript using the .focus() method.
Example :
Here is a menu that is declared ahead of the menu button. If you tab onto the button and hit enter, the menu is revealed. But your tab focus is still on the menu button, so your next [TAB] will take you somewhere else. We fix it by setting the focus on the first menu item after opening the menu.
<script><br />
function displayMenu(value) {<br />
document.getElementById("custommenu").style.display=value;<br />
}<br />
</script><div id="custommenu" style="display:none ;"> <button id="item1" onclick="displayMenu(’none’) ;">Menu item1</button> <button id="item2" onclick="displayMenu(’none’) ;">Menu item2</button> </div> <button onclick="displayMenu(’block’) ;">Menu</button> <script> function displayMenu(value) document.getElementById("custommenu").style.display=value ; </script>
<script><br />
function displayMenu2(value) {<br />
document.getElementById("custommenu2").style.display=value;<br />
document.getElementById("item1").focus();<br />
}<br />
</script><div id="custommenu" style="display:none ;"> <button id="item1" onclick="displayMenu(’none’) ;">Menu item1</button> <button id="item2" onclick="displayMenu(’none’) ;">Menu item2</button> </div> <button onclick="displayMenu(’block’) ;">Menu</button> <script> function displayMenu(value) document.getElementById("custommenu").style.display=value ; document.getElementById("item1").focus() ; </script>
You will notice that there are still some things you can improve on here. For example, after you close the menu again with one of the menu items, the focus does not move back onto the menu button.
Also, after opening the menu, you may prefer not to move the focus onto the first menu item but rather just onto the menu <div>. You can do so by giving that div a @tabindex and then calling .focus() on it. If you do not want to make the div part of the normal tabbing order, just give it a @tabindex=-1 value. This will allow your div to receive focus from script, but be exempt from accidental tabbing onto (though usually you just want to use @tabindex=0).
Bonus : If you want to help keyboard users even more, you can also put outlines on the element that is currently in focus using CSS”s outline property. If you want to avoid the outlines for mouse users, you can dynamically add a class that removes the outline in mouseover events but leaves it for :focus.
2.5. Provide sensible keyboard shortcuts
At this stage your application is actually keyboard accessible. Congratulations !
However, it’s still not very efficient : like power-users, screenreader users love keyboard shortcuts : can you imagine if you were forced to tab through an entire page, or navigate back to a menu tree at the top of the page, to reach each control you were interested in ? And, obviously, anything which makes navigating the app via the keyboard more efficient for screenreader users will benefit all power users as well, like the ubiquitous keyboard shortcuts for cut, copy and paste.
HTML4 introduced so-called accesskeys for this. In HTML5 @accesskey is now allowed on all elements.
The @accesskey attribute takes the value of a keyboard key (e.g. @accesskey="x") and is activated through platform- and browser-specific activation keys. For example, on the Mac it’s generally the [Ctrl] key, in IE it’ the [Alt] key, in Firefox on Windows [Shift]-[Alt], and in Opera on Windows [Shift]-[ESC]. You press the activation key and the accesskey together which either activates or focuses the element with the @accesskey attribute.
Example :
<script><br />
var button = document.getElementById('accessbutton');<br />
if (button.accessKeyLabel) {<br />
button.innerHTML += ' (' + button.accessKeyLabel + ')';<br />
}<br />
</script><button id="accessbutton" onclick="alert(’sent !’)" accesskey="e"> Send </button> <script> var button = document.getElementById(’accessbutton’) ; if (button.accessKeyLabel) button.innerHTML += ’ (’ + button.accessKeyLabel + ’)’ ; </script>
Now, the idea behind this is clever, but the execution is pretty poor. Firstly, the different activation keys between different platforms and browsers make it really hard for people to get used to the accesskeys. Secondly, the key combinations can conflict with browser and screenreader shortcut keys, the first of which will render browser shortcuts unusable and the second will effectively remove the accesskeys.
In the end it is up to the Web application developer whether to use the accesskey attribute or whether to implement explicit shortcut keys for the application through key event handlers on the window object. In either case, make sure to provide a help list for your shortcut keys.
Also note that a page with a really good hierarchical heading layout and use of ARIA landmarks can help to eliminate the need for accesskeys to jump around the page, since there are typically default navigations available in screen readers to jump directly to headings, hyperlinks, and ARIA landmarks.
3. Provide markup for AT
Having made the application keyboard accessible also has advantages for screenreaders, since they can now reach the controls individually and activate them. So, next we will use a screenreader and close our eyes to find out where we only provide visual cues to understand the necessary interaction.
Here are some of the issues to consider :
- Role may need to get identified
- States may need to be kept track of
- Properties may need to be made explicit
- Labels may need to be provided for elements
This is where the W3C’s ARIA (Accessible Rich Internet Applications) standard comes in. ARIA attributes provide semantic information to screen readers and other AT that is otherwise conveyed only visually.
Note that using ARIA does not automatically implement the standard widget behavior – you’ll still need to add focus management, keyboard navigation, and change aria attribute values in script.
3.1. ARIA roles
After implementing a custom interactive widget, you need to add a @role attribute to indicate what type of controls it is, e.g. that it is playing the role of a standard tag such as a button.
Example :
This menu button is implemented as a <div>, but with a role of “button” it is announced as a button by a screenreader.
<div tabindex="0" role="button">Menu</div>
ARIA roles also describe composite controls that do not have a native HTML equivalent.
Example :
This menu with menu items is implemented as a set of <div> tags, but with a role of “menu” and “menuitem” items.
<div role="menu"> <div tabindex="0" role="menuitem">Cut</div> <div tabindex="0" role="menuitem">Copy</div> <div tabindex="0" role="menuitem">Paste</div> </div>
3.2. ARIA states
Some interactive controls represent different states, e.g. a checkbox can be checked or unchecked, or a menu can be expanded or collapsed.
Example :
The following menu has states on the menu items, which are here not just used to give an aural indication through the screenreader, but also a visual one through CSS.
<style> .custombutton[aria-checked=true]:before content : "\2713 " ; </style> <div role="menu"> <div tabindex="0" role="menuitem" aria-checked="true">Left</div> <div tabindex="0" role="menuitem" aria-checked="false">Center</div> <div tabindex="0" role="menuitem" aria-checked="false">Right</div> </div>
3.3. ARIA properties
Some of the functionality of interactive controls cannot be captured by the role attribute alone. We have ARIA properties to add features that the screenreader needs to announce, such as aria-label, aria-haspopup, aria-activedescendant, or aria-live.
Example :
The following drop-down menu uses aria-haspopup to tell the screenreader that there is a popup hidden behind the menu button together with an ARIA state of aria-expanded to track whether it’s open or closed.
<script><br />
var button = document.getElementById("button");<br />
var menu = document.getElementById("menu");<br />
var items = document.getElementsByClassName("menuitem");<br />
var focused = 0;<br />
function showMenu(evt) {<br />
evt.stopPropagation();<br />
menu.style.visibility = 'visible';<br />
button.setAttribute('aria-expanded','true');<br />
focused = getSelected();<br />
items[focused].focus();<br />
}<br />
function hideMenu(evt) {<br />
evt.stopPropagation();<br />
menu.style.visibility = 'hidden';<br />
button.setAttribute('aria-expanded','false');<br />
button.focus();<br />
}<br />
function getSelected() {<br />
for (var i=0; i < items.length; i++) {<br />
if (items[i].getAttribute('aria-checked') == 'true') {<br />
return i;<br />
}<br />
}<br />
}<br />
function setSelected(elem) {<br />
var curSelected = getSelected();<br />
items[curSelected].setAttribute('aria-checked', 'false');<br />
elem.setAttribute('aria-checked', 'true');<br />
}<br />
function selectItem(evt) {<br />
setSelected(evt.target);<br />
hideMenu(evt);<br />
}<br />
function getPrevItem(index) {<br />
var prev = index - 1;<br />
if (prev < 0) {<br />
prev = items.length - 1;<br />
}<br />
return prev;<br />
}<br />
function getNextItem(index) {<br />
var next = index + 1;<br />
if (next == items.length) {<br />
next = 0;<br />
}<br />
return next;<br />
}<br />
function handleButtonKeys(evt) {<br />
evt.stopPropagation();<br />
var key = evt.keyCode;<br />
switch(key) {<br />
case (13): /* ENTER */<br />
case (32): /* SPACE */<br />
showMenu(evt);<br />
default:<br />
}<br />
}<br />
function handleMenuKeys(evt) {<br />
evt.stopPropagation();<br />
var key = evt.keyCode;<br />
switch(key) {<br />
case (38): /* UP */<br />
focused = getPrevItem(focused);<br />
items[focused].focus();<br />
break;<br />
case (40): /* DOWN */<br />
focused = getNextItem(focused);<br />
items[focused].focus();<br />
break;<br />
case (13): /* ENTER */<br />
case (32): /* SPACE */<br />
setSelected(evt.target);<br />
hideMenu(evt);<br />
break;<br />
case (27): /* ESC */<br />
hideMenu(evt);<br />
break;<br />
default:<br />
}<br />
}<br />
button.addEventListener('click', showMenu, false);<br />
button.addEventListener('keydown', handleButtonKeys, false);<br />
for (var i = 0; i < items.length; i++) {<br />
items[i].addEventListener('click', selectItem, false);<br />
items[i].addEventListener('keydown', handleMenuKeys, false);<br />
}<br />
</script><div class="custombutton" id="button" tabindex="0" role="button" aria-expanded="false" aria-haspopup="true"> <span>Justify</span> </div> <div role="menu" class="menu" id="menu" style="display : none ;"> <div tabindex="0" role="menuitem" class="menuitem" aria-checked="true"> Left </div> <div tabindex="0" role="menuitem" class="menuitem" aria-checked="false"> Center </div> <div tabindex="0" role="menuitem" class="menuitem" aria-checked="false"> Right </div> </div> [CSS and JavaScript for example omitted]
3.4. Labelling
The main issue that people know about accessibility seems to be that they have to put alt text onto images. This is only one means to provide labels to screenreaders for page content. Labels are short informative pieces of text that provide a name to a control.
There are actually several ways of providing labels for controls :
- on img elements use @alt
- on input elements use the label element
- use @aria-labelledby if there is another element that contains the label
- use @title if you also want a label to be used as a tooltip
- otherwise use @aria-label
I’ll provide examples for the first two use cases - the other use cases are simple to deduce.
Example :
The following two images show the rough concept for providing alt text for images : images that provide information should be transcribed, images that are just decorative should receive an empty @alt attribute.
Image by Noah Sussman<img src="texture.jpg" alt=""> <img src="lolcat.jpg" alt="shocked lolcat titled ’HTML cannot do that !"> <img src="texture.jpg" alt="">
When marking up decorative images with an empty @alt attribute, the image is actually completely removed from the accessibility tree and does not confuse the blind user. This is a desired effect, so do remember to mark up all your images with @alt attributes, even those that don’t contain anything of interest to AT.
Example :
In the example form above in Section 2.3, when tabbing directly on the input elements, the screen reader will only say "edit text" without announcing what meaning that text has. That’s not very useful. So let’s introduce a label element for the input elements. We’ll also add checkboxes with a label.
<label>Doctor title :</label> <input type="checkbox" id="doctor"/> <label>Firstname :</label> <input type="text" id="firstname2"/>
<label for="lastname2">Lastname :</label>
<input type="text" id="lastname2"/><label>Address :
<input type="text" id="address2">
</label>
<label for="city2">City :
<input type="text" id="city2">
</label>
<label for="remember">Remember me :</label>
<input type="checkbox" id="remember">In this example we use several different approaches to show what a different it makes to use the <label> element to mark up input boxes.
The first two fields just have a <label> element next to a <input> element. When using a screenreader you will not notice a difference between this and not using the <label> element because there is no connection between the <label> and the <input> element.
In the third field we use the @for attribute to create that link. Now the input field isn’t just announced as "edit text", but rather as "Lastname edit text", which is much more useful. Also, the screenreader can now skip the labels and get straight on the input element.
In the fourth and fifth field we actually encapsulate the <input> element inside the <label> element, thus avoiding the need for a @for attribute, though it doesn’t hurt to explicity add it.
Finally we look at the checkbox. By including a referenced <label> element with the checkbox, we change the screenreaders announcement from just "checkbox not checked" to "Remember me checkbox not checked". Also notice that the click target now includes the label, making the checkbox not only more usable to screenreaders, but also for mouse users.
4. Conclusions
This article introduced a process that you can follow to make your Web applications accessible. As you do that, you will noticed that there are other things that you may need to do in order to give the best experience to a power user on a keyboard, a blind user using a screenreader, or a vision-impaired user using a screen magnifier. But once you’ve made a start, you will notice that it’s not all black magic and a lot can be achieved with just a little markup.
You will find more markup in the WAI ARIA specification and many more resources at Mozilla’s ARIA portal. Now go and change the world !
Many thanks to Alice Boxhall and Dominic Mazzoni for their proof-reading and suggested changes that really helped improve the article !
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Google Analytics Now Illegal in Austria ; Other EU Member States Expected to Follow
18 janvier 2022, par Erin — Privacy -
WebVTT as a W3C Recommendation
2 décembre 2013, par silviaThree weeks ago I attended TPAC, the annual meeting of W3C Working Groups. One of the meetings was of the Timed Text Working Group (TT-WG), that has been specifying TTML, the Timed Text Markup Language. It is now proposed that WebVTT be also standardised through the same Working Group.
How did that happen, you may ask, in particular since WebVTT and TTML have in the past been portrayed as rival caption formats ? How will the WebVTT spec that is currently under development in the Text Track Community Group (TT-CG) move through a Working Group process ?
I’ll explain first why there is a need for WebVTT to become a W3C Recommendation, and then how this is proposed to be part of the Timed Text Working Group deliverables, and finally how I can see this working between the TT-CG and the TT-WG.
Advantages of a W3C Recommendation
TTML is a XML-based markup format for captions developed during the time that XML was all the hotness. It has become a W3C standard (a so-called “Recommendation”) despite not having been implemented in any browsers (if you ask me : that’s actually a flaw of the W3C standardisation process : it requires only two interoperable implementations of any kind – and that could be anyone’s JavaScript library or Flash demonstrator – it doesn’t actually require browser implementations. But I digress…). To be fair, a subpart of TTML is by now implemented in Internet Explorer, but all the other major browsers have thus far rejected proposals of implementation.
Because of its Recommendation status, TTML has become the basis for several other caption standards that other SDOs have picked : the SMPTE’s SMPTE-TT format, the EBU’s EBU-TT format, and the DASH Industry Forum’s use of SMPTE-TT. SMPTE-TT has also become the “safe harbour” format for the US legislation on captioning as decided by the FCC. (Note that the FCC requirements for captions on the Web are actually based on a list of features rather than requiring a specific format. But that will be the topic of a different blog post…)
WebVTT is much younger than TTML. TTML was developed as an interchange format among caption authoring systems. WebVTT was built for rendering in Web browsers and with HTML5 in mind. It meets the requirements of the <track> element and supports more than just captions/subtitles. WebVTT is popular with browser developers and has already been implemented in all major browsers (Firefox Nightly is the last to implement it – all others have support already released).
As we can see and as has been proven by the HTML spec and multiple other specs : browsers don’t wait for specifications to have W3C Recommendation status before they implement them. Nor do they really care about the status of a spec – what they care about is whether a spec makes sense for the Web developer and user communities and whether it fits in the Web platform. WebVTT has obviously achieved this status, even with an evolving spec. (Note that the spec tries very hard not to break backwards compatibility, thus all past implementations will at least be compatible with the more basic features of the spec.)
Given that Web browsers don’t need WebVTT to become a W3C standard, why then should we spend effort in moving the spec through the W3C process to become a W3C Recommendation ?
The modern Web is now much bigger than just Web browsers. Web specifications are being used in all kinds of devices including TV set-top boxes, phone and tablet apps, and even unexpected devices such as white goods. Videos are increasingly omnipresent thus exposing deaf and hard-of-hearing users to ever-growing challenges in interacting with content on diverse devices. Some of these devices will not use auto-updating software but fixed versions so can’t easily adapt to new features. Thus, caption producers (both commercial and community) need to be able to author captions (and other video accessibility content as defined by the HTML5
Understandably, device vendors in this space have a need to build their technology on standardised specifications. SDOs for such device technologies like to reference fixed specifications so the feature set is not continually updating. To reference WebVTT, they could use a snapshot of the specification at any time and reference that, but that’s not how SDOs work. They prefer referencing an officially sanctioned and tested version of a specification – for a W3C specification that means creating a W3C Recommendation of the WebVTT spec.
Taking WebVTT on a W3C recommendation track is actually advantageous for browsers, too, because a test suite will have to be developed that proves that features are implemented in an interoperable manner. In summary, I can see the advantages and personally support the effort to take WebVTT through to a W3C Recommendation.
Choice of Working Group
FAIK this is the first time that a specification developed in a Community Group is being moved into the recommendation track. This is something that has been expected when the W3C created CGs, but not something that has an established process yet.
The first question of course is which WG would take it through to Recommendation ? Would we create a new Working Group or find an existing one to move the specification through ? Since WGs involve a lot of overhead, the preference was to add WebVTT to the charter of an existing WG. The two obvious candidates were the HTML WG and the TT-WG – the first because it’s where WebVTT originated and the latter because it’s the closest thematically.
Adding a deliverable to a WG is a major undertaking. The TT-WG is currently in the process of re-chartering and thus a suggestion was made to add WebVTT to the milestones of this WG. TBH that was not my first choice. Since I’m already an editor in the HTML WG and WebVTT is very closely related to HTML and can be tested extensively as part of HTML, I preferred the HTML WG. However, adding WebVTT to the TT-WG has some advantages, too.
Since TTML is an exchange format, lots of captions that will be created (at least professionally) will be in TTML and TTML-related formats. It makes sense to create a mapping from TTML to WebVTT for rendering in browsers. The expertise of both, TTML and WebVTT experts is required to develop a good mapping – as has been shown when we developed the mapping from CEA608/708 to WebVTT. Also, captioning experts are already in the TT-WG, so it helps to get a second set of eyes onto WebVTT.
A disadvantage of moving a specification out of a CG into a WG is, however, that you potentially lose a lot of the expertise that is already involved in the development of the spec. People don’t easily re-subscribe to additional mailing lists or want the additional complexity of involving another community (see e.g. this email).
So, a good process needs to be developed to allow everyone to contribute to the spec in the best way possible without requiring duplicate work. How can we do that ?
The forthcoming process
At TPAC the TT-WG discussed for several hours what the next steps are in taking WebVTT through the TT-WG to recommendation status (agenda with slides). I won’t bore you with the different views – if you are keen, you can read the minutes.
What I came away with is the following process :
- Fix a few more bugs in the CG until we’re happy with the feature set in the CG. This should match the feature set that we realistically expect devices to implement for a first version of the WebVTT spec.
- Make a FSA (Final Specification Agreement) in the CG to create a stable reference and a clean IPR position.
- Assuming that the TT-WG’s charter has been approved with WebVTT as a milestone, we would next bring the FSA specification into the TT-WG as FPWD (First Public Working Draft) and immediately do a Last Call which effectively freezes the feature set (this is possible because there has already been wide community review of the WebVTT spec) ; in parallel, the CG can continue to develop the next version of the WebVTT spec with new features (just like it is happening with the HTML5 and HTML5.1 specifications).
- Develop a test suite and address any issues in the Last Call document (of course, also fix these issues in the CG version of the spec).
- As per W3C process, substantive and minor changes to Last Call documents have to be reported and raised issues addressed before the spec can progress to the next level : Candidate Recommendation status.
- For the next step – Proposed Recommendation status – an implementation report is necessary, and thus the test suite needs to be finalized for the given feature set. The feature set may also be reduced at this stage to just the ones implemented interoperably, leaving any other features for the next version of the spec.
- The final step is Recommendation status, which simply requires sufficient support and endorsement by W3C members.
The first version of the WebVTT spec naturally has a focus on captioning (and subtitling), since this has been the dominant use case that we have focused on this far and it’s the part that is the most compatibly implemented feature set of WebVTT in browsers. It’s my expectation that the next version of WebVTT will have a lot more features related to audio descriptions, chapters and metadata. Thus, this seems a good time for a first version feature freeze.
There are still several obstacles towards progressing WebVTT as a milestone of the TT-WG. Apart from the need to get buy-in from the TT-WG, the TT-CG, and the AC (Adivisory Committee who have to approve the new charter), we’re also looking at the license of the specification document.
The CG specification has an open license that allows creating derivative work as long as there is attribution, while the W3C document license for documents on the recommendation track does not allow the creation of derivative work unless given explicit exceptions. This is an issue that is currently being discussed in the W3C with a proposal for a CC-BY license on the Recommendation track. However, my view is that it’s probably ok to use the different document licenses : the TT-WG will work on WebVTT 1.0 and give it a W3C document license, while the CG starts working on the next WebVTT version under the open CG license. It probably actually makes sense to have a less open license on a frozen spec.
Making the best of a complicated world
WebVTT is now proposed as part of the recharter of the TT-WG. I have no idea how complicated the process will become to achieve a W3C WebVTT 1.0 Recommendation, but I am hoping that what is outlined above will be workable in such a way that all of us get to focus on progressing the technology.
At TPAC I got the impression that the TT-WG is committed to progressing WebVTT to Recommendation status. I know that the TT-CG is committed to continue developing WebVTT to its full potential for all kinds of media-time aligned content with new kinds already discussed at FOMS. Let’s enable both groups to achieve their goals. As a consequence, we will allow the two formats to excel where they do : TTML as an interchange format and WebVTT as a browser rendering format.