Wednesday, March 27, 2013

Accessible Mozilla: Tech overview of Firefox 21

Next week Firefox 21 reaches a beta status so it's time to list accessibility related changes we introduced for assistive technology. This release we were focused on under-the-hood improvements and ARIA bugs. Let's start.


* We pick up accessible value of ARIA combobox in name computation. An example:

  <label for="test">Flash the screen 
    <div role="combobox">
      <div role="textbox"></div>
      <ul role="listbox" style="list-style-type:none;">
        <li role="option">1</li>
        <li role="option" aria-selected="true">2</li>
        <li role="option">3</li>

In this case accessible name of the label is "Flash the screen 2 times" (refer to bug).

* ARIA grid has editable state by default. ARIA grid editable or readonly states (a case of aria-readonly attribute usage) are inherited by grid cells until aria-readonly attribute on a gridcell overrides it (see bug).

* We no longer expose hidden:false object attribute for aria-hidden="false" because ARIA group members concluded that aria-hidden mirrors CSS display:none (check out the bug for details). In particular this means

  <div aria-hidden="true">
    <input aria-hidden="false">

HTML input element is still ARIA hidden.

Sure the author doesn't have any single reason to use aria-hidden="false" in his web app but you know people do crazy things every time. If we exposed it then it could be confusing for screen readers (if they wouldn't know that "false" value is an author error of course). However you may ask why ARIA spec doesn't like to treat "false" value as "true" value like it does for any other error value. It's less work for browsers, no burden for AT. You see that wouldn't bad. I do not know. Go ask your dad.

* We supported ARIA based text attributes. Now you can use aria-invalid="grammar" to mark that your text has a grammatical error. From AT perspective it means that we expose invalid:grammar text attribute.

Unfortunately ARIA spec doesn't look perfect about defining the aria-invalid. For example, it doesn't allow a list of values

  <p aria-invalid="spelling,grammar">my wrong text</p>

and it says nothing about aria-invalid inheritance which would allow you to do a trick

  <p aria-invalid="spelling">
    <span aria-invalid="grammar">my wrong text</span>

to say that your text is misspelled and has grammatical error. Also it doesn't say how the browser should resolve collisions between aria-invalid and native spelling support which is also mapped into invalid text attribute.


* HTML5 main element was implemented. It's exposed as xml-roles:main object attribute on accessibility layer.

* We sorted out name computation for HTML input buttons:
  • HTML input@type="button", @type="submit", type="reset" gets name from:
    • @value attribute
    • @title attribute 
  • HTML input@type="image" gets name from:
    • @alt attribute
    • @value attribute
    • @title attribute
  • HTML input@type="image" having no valid @src attribute gets name from:
    • @alt attribute
    • @value attribute
    • "Submit Query" - a visible label of the button

Everything else

* We did one more fix in our name computation algorithm and now we don't jam together a plain text and name coming from a control element. For example:

  <label>foo<input type="text" value="bar">baz</label>

The accessible name of the label is "foo bar baz". Visually "foo" and "baz" are separated from HTML input, thus we wrap the control's name by spaces when we compute the label name.

* We learned how to coalesce state change events so you should get only one event when the object changes its state fast enough, for example, it may happen during document loading when state busy of a document accessible is switched quickly.

* You can use magic offsets now to get text attributes.

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