Revision 593637 of Mobile accessibility checklist

<div class="summary">
 <p><span class="seoSummary">This document provides a concise checklist of accessibility requirements for mobile app developers. It is intended to continuously evolve as more patterns arise.</span></p>
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<h2 id="Colour">Colour</h2>
<ul>
 <li>Colour contrast <strong>MUST</strong> comply with <a href="https://www.w3.org/TR/WCAG/">WCAG 2.0</a> AA level requirements:
  <ul>
   <li>Contrast ratio of 4.5:1 for normal text (less than 18 point or 14 point bold.)</li>
   <li>Contrast ratio of 3:1 for large text (at least 18 point or 14 point bold.)</li>
  </ul>
 </li>
 <li>Information conveyed via colour <strong>MUST</strong> be also available by other means too (underlined text for links, etc.)</li>
</ul>
<div class="note">
 <p><strong>Note</strong>: Jon Snook has written a useful <a href="https://snook.ca/technical/colour_contrast/colour.html">Colour Contrast Checker</a> that is useful for checking contrast between a background and foreground colour. Alternatively, the <a href="https://contrast-finder.tanaguru.com/">Tanaguru Contrast-Finder</a> does a similar job, but also suggests similar but better contrasting colours for you to consider using.</p>
</div>
<h2 id="Visibility">Visibility</h2>
<ul>
 <li>Content hiding techniques such as zero opacity, z-index order and off-screen placement <strong>MUST NOT</strong> be used exclusively to handle visibility.</li>
 <li>Everything other than the currently visible screen <strong>MUST</strong> be <em>truly</em> invisible (especially relevant for single page apps with multiple <em>cards</em>):
  <ul>
   <li><strong>USE</strong> the <code>hidden</code> attribute or <code>visibility</code> or <code>display</code> style properties.</li>
   <li>Unless absolutely unavoidable, <code>aria-hidden</code> attribute <strong>SHOULD NOT</strong> be used.</li>
  </ul>
 </li>
</ul>
<h2 id="Focus">Focus</h2>
<ul>
 <li>All activatable elements <strong>MUST</strong> be focusable:
  <ul>
   <li>Standard controls such as links, buttons, and form fields are focusable by default.</li>
   <li>Non-standard controls <strong>MUST</strong> have an appropriate <a href="https://www.w3.org/TR/wai-aria/roles">ARIA Role</a> assigned to them, such as <code>button</code>, <code>link</code>, or <code>checkbox</code>.</li>
  </ul>
 </li>
 <li>Focus should be handled in a logical order and consistent manner.</li>
</ul>
<h2 id="Text_Equivalents">Text Equivalents</h2>
<ul>
 <li>Text equivalent <strong>MUST</strong> be provided for every non-strictly presentational non-text element within the app.
  <ul>
   <li>Use <em>alt</em> and <em>title</em> where appropriate (<em>s</em>ee Steve Faulkner's post about <a href="https://blog.paciellogroup.com/2013/01/using-the-html-title-attribute-updated/">Using the HTML title attribute</a> for a good guide.)</li>
   <li>If the above attributes are not applicable, use appropriate <a href="https://www.w3.org/WAI/PF/aria/states_and_properties#global_states_header">ARIA Properties</a> such as <code>aria-label</code>, <code>aria-labelledby</code>, or <code>aria-describedby</code>.</li>
  </ul>
 </li>
 <li>Images of text <strong>MUST</strong> be avoided.</li>
 <li>All form controls <strong>MUST</strong> have labels ({{ htmlelement("label") }} elements) for the benefit of screen reader users.</li>
</ul>
<h2 id="Handling_State">Handling State</h2>
<ul>
 <li>Standard controls such as radio buttons and checkboxes are handled by the operating system. However, for other custom controls state changes must be provided via <a href="https://www.w3.org/TR/wai-aria/states_and_properties#attrs_widgets_header">ARIA States</a> such as<code> aria-checked</code>, <code>aria-disabled</code>, <code>aria-selected</code>, <code>aria-expanded</code>, and <code>aria-pressed</code>.</li>
</ul>
<h2 id="General_Guidelines">General Guidelines</h2>
<ul>
 <li>An app title <strong>MUST</strong> be provided.</li>
 <li>Headings <strong>MUST</strong> not break hierarchical structure
  <pre class="brush: html">
&lt;h1&gt;Top level heading&lt;/h1&gt;
  &lt;h2&gt;Secondary heading&lt;/h2&gt;
  &lt;h2&gt;Another secondary heading&lt;/h2&gt;
    &lt;h3&gt;Low level heading&lt;/h3&gt;</pre>
 </li>
 <li><a href="https://www.w3.org/TR/wai-aria/roles#landmark_roles_header">ARIA Landmark Roles</a> <strong>SHOULD</strong> be used to describe an app or document structure, such as <code>banner</code>, <code>complementary</code>, <code>contentinfo</code>, <code>main</code>, <code>navigation</code>, <code>search</code>.</li>
 <li>Touch event handlers <strong>MUST</strong> only be triggered on the <code>touchend</code> event.</li>
 <li>Touch targets <strong>MUST</strong> be large enough for the user to interact with (see the <a href="https://www.bbc.co.uk/guidelines/futuremedia/accessibility/mobile/design/touch-target-size">BBC Mobile Accessibility Guidelines</a> for useful touch target size guidelines.)</li>
</ul>
<div class="note">
 <p><strong>Note</strong>: <a href="https://www.tanaguru.com/">Tanaguru's automated accessibility testing service</a> provides a useful way to uncover some of the accessibility errors that can occur on a web page, or installed web app (e.g. Firefox OS.) You can find more about the technical implementation of Tanaguru, as well as how to contribute to the project, at <a href="https://tanaguru.org/">tanaguru.org</a>.</p>
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<div class="note">
 <p><strong>Note</strong>: The <a href="https://yzen.github.io/2014/04/30/mobile-accessibility-checklist.html">original version of this document</a> was written by <a href="https://yzen.github.io/">Yura Zenevich</a>.</p>
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