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1744 lines
91 KiB
1744 lines
91 KiB
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<p><a href="http://www.w3.org/"><img src="http://www.w3.org/Icons/w3c_home" alt="W3C" height="48" width="72" /></a></p>
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<h1><a id="title" name="title">Mobile Web Application Best Practices</a></h1>
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<h2><a id="w3c-doctype" name="w3c-doctype">W3C Recommendation 14 December 2010</a></h2>
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<dl>
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<dt>This version:</dt>
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<dd><a href="http://www.w3.org/TR/2010/REC-mwabp-20101214/">http://www.w3.org/TR/2010/REC-mwabp-20101214/</a></dd>
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<dt>Latest version:</dt>
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<dd><a href="http://www.w3.org/TR/mwabp/">http://www.w3.org/TR/mwabp/</a></dd>
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<dt>Previous version:</dt>
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<dd><a href="http://www.w3.org/TR/2010/PR-mwabp-20101021/">http://www.w3.org/TR/2010/PR-mwabp-20101021/</a></dd>
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<dt>Editors:</dt>
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<dd>Adam Connors, Google</dd>
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<dd>Bryan Sullivan, AT&T (until 2008)</dd>
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</dl>
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<p>Please refer to the <a href="http://www.w3.org/2010/12/mwabp-errata.html"><strong>errata</strong></a> for this document, which may include some normative corrections.</p>
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<p>See also <a href="http://www.w3.org/2003/03/Translations/byTechnology?technology=mwabp"><strong>translations</strong></a>.</p>
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<p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> ©2010 <a href="http://www.w3.org/"><acronym title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup> (<a href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute of Technology">MIT</acronym></a>, <a href="http://www.ercim.eu/"><acronym title="European Research Consortium for Informatics and Mathematics">ERCIM</acronym></a>, <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document use</a> rules apply.</p>
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</div>
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<hr />
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<div>
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<h2><a id="abstract" name="abstract">Abstract</a></h2>
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<p>The goal of this document is to aid the development of rich and dynamic mobile Web applications. It collects the most relevant engineering practices, promoting those that enable a better user experience and warning against those that are considered harmful.</p>
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<h2><a id="status" name="status">Status of This Document</a></h2>
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<p><em>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 <a href="http://www.w3.org/TR/">W3C technical reports index</a> at http://www.w3.org/TR/.</em></p>
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<p>This is the <strong>W3C Recommendation</strong> of Mobile Web Application Best Practices. This document was developed by the <a href="http://www.w3.org/2005/MWI/BPWG/">Mobile Web Best Practices Working Group</a> as part of the <a href="http://www.w3.org/Mobile/">Mobile Web Initiative</a>.</p>
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<p>Since publication as a Proposed Recommendation on <a href="http://www.w3.org/TR/2010/PR-mwabp-20101021/" title="W3C Proposed Recommendation of the Mobile Web Application Best Practices">21 October 2010</a>, the Working Group clarified that alternative compression formats (such as EXI) referred to in section <a href="#bp-conserve-compress">3.4.1 Use Transfer Compression</a> may not share some of the impediments of common compression formats. A <a href="diff.html" title="Differences between Proposed Recommendation and Recommendation of Mobile Web Application Best Practices">diff version</a> is available. No substantive change has been made.</p>
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<p>The document contains statements that may be regarded as forward-looking when this document is published (14 December 2010). Examples provided in the <em>How to do it</em> sections sometimes reference on-going works on technologies that the Working Group expects to become prevalent in the development community soon. These sections should be taken with a grain of salt, depending on the actual evolution of these technologies. The best practices statements should remain valid in any case. An <a href="http://www.w3.org/2010/07/mwabp-implementation-report.html">implementation report</a> is available.</p>
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<p>Comments on this specification may be sent to <a href="mailto:public-bpwg-comments@w3.org">public-bpwg-comments@w3.org</a> (with <a href="http://lists.w3.org/Archives/Public/public-bpwg-comments/">public archive</a>).</p>
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<p>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.</p>
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<p>This document was produced by a group operating under the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent Policy</a>. This document is informative only. W3C maintains a <a rel="disclosure" href="http://www.w3.org/2004/01/pp-impl/37584/status">public list of any patent disclosures</a> made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the W3C Patent Policy</a>.</p>
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<div class="toc">
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<h2><a id="contents" name="contents">Table of Contents</a></h2>
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<p class="toc">1 <a href="#introduction">Introduction</a> <br />
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1.1 <a href="#purpose">Purpose of the Document</a> <br />
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1.2 <a href="#audience">Audience</a> <br />
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1.3 <a href="#scope">Scope</a> <br />
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1.3.1 <a href="#goal">Best Practices</a> <br />
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1.3.2 <a href="#webapp-defined">Web Application</a> <br />
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1.3.3 <a href="#mobile-context">Mobile Context</a> <br />
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1.3.4 <a href="#delivery-context">Delivery Context</a> <br />
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1.4 <a href="#relationship">Relationship to other Best Practices and
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recommendations</a> <br />
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1.5 <a href="#terminology">Terminology</a> <br />
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2 <a href="#structure">Structure of Best Practice Statements</a> <br />
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3 <a href="#bp">Best Practice Statements</a> <br />
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3.1 <a href="#bp-applicationdata">Application Data</a> <br />
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3.1.1 <a href="#bp-data-cookies">Use Cookies Sparingly</a> <br
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/>
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3.1.2 <a href="#bp-data-html5">Use Appropriate Client-Side
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Storage Technologies for Local Data</a> <br />
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3.1.3 <a href="#bp-data-server">Replicate Local Data</a> <br />
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3.2 <a href="#bp-security">Security and privacy</a> <br />
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3.2.1 <a href="#bp-security-json">Do not Execute Unescaped or
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Untrusted JSON data</a> <br />
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3.3 <a href="#bp-inform-control">User Awareness and Control</a> <br />
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3.3.1 <a href="#bp-inform-personalinfo">Ensure the User is
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Informed About Use of Personal and Device Information</a> <br />
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3.3.2 <a href="#bp-enable-automatic-login">Enable Automatic
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Sign-in</a> <br />
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3.4 <a href="#bp-conserve">Conservative use of resources</a> <br />
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3.4.1 <a href="#bp-conserve-compress">Use Transfer
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Compression</a> <br />
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3.4.2 <a href="#bp-conserve-contentsize">Minimize Application
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and Data Size</a> <br />
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3.4.3 <a href="#bp-redirect-minimize">Avoid Redirects</a> <br />
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3.4.4 <a href="#bp-conserve-requests">Optimize Network
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Requests</a> <br />
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3.4.5 <a href="#bp-conserve-ext-files">Minimize External
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Resources</a> <br />
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3.4.6 <a href="#bp-conserve-sprites">Aggregate Static Images
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into a Single Composite Resource (Sprites)</a> <br />
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3.4.7 <a href="#bp-conserve-css-images">Include Background
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Images Inline in CSS Style Sheets</a> <br />
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3.4.8 <a href="#bp-conserve-fingerprint">Cache Resources By
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Fingerprinting Resource References</a> <br />
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3.4.9 <a href="#bp-conserve-ajax">Cache AJAX Data</a> <br />
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3.4.10 <a href="#bp-conserve-cookie">Do not Send Cookie
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Information Unnecessarily</a> <br />
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3.4.11 <a href="#bp-conserve-dom">Keep DOM Size
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Reasonable</a><br />
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3.5 <a href="#bp-presentation">User Experience</a> <br />
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3.5.1 <a href="#bp-presentation-startup">Optimize For
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Application Start-up Time</a><br />
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3.5.2 <a href="#bp-presentation-perceived">Minimize Perceived
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Latency</a> <br />
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3.5.3 <a href="#bp-presentation-interaction">Design for
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Multiple Interaction Methods</a> <br />
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3.5.4 <a href="#bp-presentation-focus">Preserve Focus on
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Dynamic Page Updates</a> <br />
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3.5.5 <a href="#bp-presentation-fragment">Use Fragment IDs to
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Drive Application View</a><br />
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3.5.6 <a href="#bp-interaction-uri-schemes">Make Telephone
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Numbers "Click-to-Call"</a> <br />
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3.5.7 <a href="#bp-presentation-flow">Ensure Paragraph Text
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Flows</a> <br />
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3.5.8 <a href="#bp-consistency">Ensure Consistency Of State
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Between Devices</a> <br />
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3.5.9 <a href="#bp-conserve-usepush">Consider Mobile Specific
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Technologies for Initiating Web Applications</a> <br />
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3.5.10 <a href="#bp-viewport">Use Meta Viewport Element To
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Identify Desired Screen Size</a> <br />
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3.6 <a href="#bp-devcap">Handling Variations in the Delivery
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Context</a> <br />
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3.6.1 <a href="#bp-devcap-detection">Prefer Server-Side
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Detection Where Possible</a> <br />
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3.6.2 <a href="#bp-devcap-scripting">Use Client-Side Detection
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When Necessary</a> <br />
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3.6.3 <a href="#bp-devcap-classify">Use Device Classification
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|
to Simplify Content Adaptation</a> <br />
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|
3.6.4 <a href="#bp-devcap-scripting-support">Support a
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|
non-JavaScript Variant if Appropriate</a> <br />
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3.6.5 <a href="#bp-devcap-user-choice">Offer Users a Choice of
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Interfaces</a> <br />
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3.7 <a href="#bp-further">Further Considerations</a> <br />
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3.7.1 <a href="#bp-canvas">Consider Use Of Canvas Element or
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SVG For Dynamic Graphics</a> <br />
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3.7.2 <a href="#bp-inform-automation">Inform the User About
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Automatic Network Access</a> <br />
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3.7.3 <a href="#bp-inform-network">Provide Sufficient Means to
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Control Automatic Network Access</a> <br />
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</p>
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<h2><a id="appendices" name="appendices">Appendices</a></h2>
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<p class="toc">Appendix 1: <a href="#dependent-properties">Best Practice
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Dependent Device Properties</a><br />
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Appendix 2: <a href="#references">References</a><br />
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2.1 <a href="#ref-mwi">MWI References</a> <br />
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2.2 <a href="#ref-dip">Device Independence</a> <br />
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2.3 <a href="#ref-web">Web, Protocols and Languages</a> <br />
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2.4 <a href="#ref-other">Other References</a> <br />
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Appendix 3: <a href="#acknowledgements">Acknowledgments</a></p>
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</div>
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<h2><a id="list-bp" name="list-bp">List of Best Practices</a></h2>
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<p>The following Best Practices are discussed in this document and listed here
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for convenience.</p>
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<ol>
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<li><p class="stmt"><a href="#bp-data-cookies">Use Cookies Sparingly</a></p>
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|
</li>
|
|
<li><p class="stmt"><a href="#bp-data-html5">Use Appropriate Client-Side
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|
Storage Technologies for Local Data</a></p>
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</li>
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|
<li><p class="stmt"><a href="#bp-data-server">Replicate Local Data</a></p>
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</li>
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|
<li><p class="stmt"><a href="#bp-security-json">Do not Execute Unescaped or
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|
Untrusted JSON data</a></p>
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|
</li>
|
|
<li><p class="stmt"><a href="#bp-inform-personalinfo">Ensure the User is
|
|
Informed About Use of Personal and Device Information</a></p>
|
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</li>
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|
<li><p class="stmt"><a href="#bp-enable-automatic-login">Enable Automatic
|
|
Sign-in</a></p>
|
|
</li>
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|
<li><p class="stmt"><a href="#bp-conserve-compress">Use Transfer
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Compression</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-conserve-contentsize">Minimize Application
|
|
and Data Size</a></p>
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</li>
|
|
<li><p class="stmt"><a href="#bp-redirect-minimize">Avoid Redirects</a></p>
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|
</li>
|
|
<li><p class="stmt"><a href="#bp-conserve-requests">Optimize Network
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|
Requests</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-conserve-ext-files">Minimize External
|
|
Resources</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-conserve-sprites">Aggregate Static Images
|
|
into a Single Composite Resource (Sprites)</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-conserve-css-images">Include Background
|
|
Images Inline in CSS Style Sheets</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-conserve-fingerprint">Cache Resources By
|
|
Fingerprinting Resource References</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-conserve-ajax">Cache AJAX Data</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-conserve-cookie">Do not Send Cookie
|
|
Information Unnecessarily</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-conserve-dom">Keep DOM Size
|
|
Reasonable</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-presentation-startup">Optimize For
|
|
Application Start-up Time</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-presentation-perceived">Minimize Perceived
|
|
Latency</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-presentation-interaction">Design for
|
|
Multiple Interaction Methods</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-presentation-focus">Preserve Focus on
|
|
Dynamic Page Updates</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-presentation-fragment">Use Fragment IDs to
|
|
Drive Application View</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-interaction-uri-schemes">Make Telephone
|
|
Numbers "Click-to-Call"</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-presentation-flow">Ensure Paragraph Text
|
|
Flows</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-consistency">Ensure Consistency Of State
|
|
Between Devices</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-conserve-usepush">Consider Mobile Specific
|
|
Technologies for Initiating Web Applications</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-viewport">Use Meta Viewport Element To
|
|
Identify Desired Screen Size</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-devcap-detection">Prefer Server-side
|
|
Detection Where Possible</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-devcap-scripting">Use Client-side Detection
|
|
When Necessary</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-devcap-classify">Use Device Classification
|
|
to Simplify Content Adaptation</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-devcap-scripting-support">Support a
|
|
non-JavaScript Variant if Appropriate</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-devcap-user-choice">Offer Users a Choice of
|
|
Interfaces</a></p>
|
|
</li>
|
|
</ol>
|
|
|
|
<p>The following advisory notes from the Mobile Web Best Practices Working
|
|
Group are also discussed in this document and listed here for convenience.</p>
|
|
<ol>
|
|
<li><p class="stmt"><a href="#bp-canvas">Consider Use Of Canvas Element or
|
|
SVG For Dynamic Graphics</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-inform-automation">Inform the User About
|
|
Automatic Network Access</a></p>
|
|
</li>
|
|
<li><p class="stmt"><a href="#bp-inform-network">Provide Sufficient Means to
|
|
Control Automatic Network Access</a></p>
|
|
</li>
|
|
</ol>
|
|
|
|
<h2><a id="introduction" name="introduction">1 Introduction</a></h2>
|
|
|
|
<h3><a id="purpose" name="purpose">1.1 Purpose of the Document</a></h3>
|
|
|
|
<p>This document sets out a series of recommendations designed to facilitate
|
|
development and delivery of Web applications on mobile devices. The
|
|
recommendations are offered to creators, maintainers and operators of mobile
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|
Web sites.</p>
|
|
|
|
<h3><a id="audience" name="audience">1.2 Audience</a></h3>
|
|
|
|
<p>Readers of this document are expected to be familiar with the creation of
|
|
Web applications, and to have a general familiarity with the technologies
|
|
involved, but are not expected to have a background in mobile technologies or
|
|
previous experience with Mobile Web Best Practices (BP1) <a
|
|
href="#MWBP">[MWBP]</a>.</p>
|
|
|
|
<p>The document is not targeted solely at developers; others, such as
|
|
interaction and graphic designers, site administrators, and tool developers are
|
|
encouraged to read it.</p>
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|
|
|
<h3><a id="scope" name="scope">1.3 Scope</a></h3>
|
|
|
|
<p>These recommendations expand on the recommendations of BP1. Where the focus
|
|
of BP1 is primarily the extension of Web <em>browsing</em> to mobile devices,
|
|
this document considers the development of Web <em>applications</em> on mobile
|
|
devices.</p>
|
|
|
|
<h4><a id="goal" name="goal">1.3.1 Best Practices</a></h4>
|
|
|
|
<p>The approach in writing this document has been to collate and present the
|
|
most relevant engineering practices prevalent in the development community
|
|
today and identify those that: a) facilitate the exploitation of device
|
|
capabilities to enable a better user experience; or b) are considered harmful
|
|
and can have non-obvious detrimental effects on the overall quality of an
|
|
application.</p>
|
|
|
|
<p>The goal of this document is not to invent or endorse future technologies.
|
|
However, there are a number of cases where explicitly omitting a Best Practice
|
|
that referred to an emerging technology on the grounds that it was too recent
|
|
to have received wide adoption would have unnecessarily excluded a valuable
|
|
recommendation. As such, some Best Practices have been included on the grounds
|
|
that the Working Group believes that they <em>will soon become</em> fully
|
|
qualified Best Practices (e.g. in prevalent use within the development
|
|
community).</p>
|
|
|
|
<p>In building a Web application, it is not necessary to implement <em>all</em>
|
|
Best Practices. Instead, each Best Practice should be considered as a possible
|
|
measure that might be implemented towards the goal of providing as rich and
|
|
dynamic an experience as possible on a mobile Web browser.</p>
|
|
|
|
<h4><a id="webapp-defined" name="webapp-defined">1.3.2 Web Application</a></h4>
|
|
|
|
<p>For the purposes of this document, the term "Web application" refers to a
|
|
Web page (XHTML or a variant thereof + CSS) or collection of Web pages
|
|
delivered over HTTP which use server-side or client-side processing (e.g.
|
|
JavaScript) to provide an "application-like" experience within a Web browser.
|
|
Web applications are distinct from simple Web content (the focus of BP1) in
|
|
that they include locally executable elements of interactivity and persistent
|
|
state.</p>
|
|
|
|
<p>While the focus of this document is the Best Practices that apply to
|
|
applications running in a Web browser, in many cases these recommendations are
|
|
equally applicable to other kinds of Web run-time, such as the W3C work on Web
|
|
Widgets [<a href="#WIDGETS">WIDGETS</a>] and also in a number of
|
|
vendor-specific initiatives.</p>
|
|
|
|
<h4><a id="mobile-context" name="mobile-context">1.3.3 Mobile Context</a></h4>
|
|
|
|
<p>In a world where the line between mobile and non-mobile is necessarily
|
|
blurred and a document that restricts its focus solely to best practices that
|
|
are <em>uniquely</em> mobile would most likely be very short. With this in
|
|
mind, the focus of this document is to address those aspects of Web application
|
|
development for which there are additional, non-trivial concerns associated
|
|
with the mobile context. This applies equally both to the limitations of the
|
|
mobile context (e.g. small screen, intermittent connectivity), and also the
|
|
additional scope and features that should be considered when developing for the
|
|
mobile context (e.g. device context / location, presence of personal data on
|
|
the device, etc).</p>
|
|
|
|
<h4 id="delivery-context">1.3.4 Delivery Context</h4>
|
|
|
|
<p>This document builds on some of the concepts described by the Ubiquitous Web
|
|
Applications Working Group (UWA) and the Device Independence Principles <a
|
|
href="#DIP">[DIP]</a>. It also discusses device and delivery channel
|
|
characteristics, which the UWA has named "Delivery Context" <a
|
|
href="#DCODI">[DCODI]</a>.</p>
|
|
|
|
<p>This document does not make any explicit assumptions about features of the
|
|
Delivery Context, but most Best Practices assume devices with support for
|
|
standard XHTML, JavaScript, and CSS capability. At the time of writing,
|
|
developers of relatively complex Web applications targeting mid- to high-end
|
|
devices are most likely to benefit from these Best Practices, but as the
|
|
technology evolves it is expected that the range of relevant devices will
|
|
increase.</p>
|
|
|
|
<p>Additionally, some Best Practices are relevant only if the device exposes
|
|
certain capabilities (for example, access to device information such as
|
|
location). In these cases the requirements are summarized as a separate
|
|
sub-heading.</p>
|
|
|
|
<p>Saying that applications should be sensitive to the Delivery Context implies
|
|
that some level of device knowledge and content adaptation is required. For
|
|
Best Practices specifically related to this area, see <a
|
|
href="#bp-devcap-detection">3.6 Handling Variations in Delivery Context</a>.</p>
|
|
|
|
<h3><a id="relationship" name="relationship">1.4 Relationship to other Best
|
|
Practices and recommendations</a></h3>
|
|
|
|
<p>These recommendations are complementary to the recommendations of Mobile Web
|
|
Best Practices 1.0 (BP1) though their focus is somewhat orthogonal. Whereas BP1
|
|
focused on delivering a good experience on a broad range of devices, this
|
|
document's focus is on making use of advanced device capabilities to deliver
|
|
the best possible experience on those devices that can support it. For this
|
|
reason, while readers of this document are likely to benefit from reading BP1
|
|
it is not a pre-requisite.</p>
|
|
|
|
<h3 id="terminology">1.5 Terminology</h3>
|
|
|
|
<p>Note that the term "JavaScript" is used in place of the (arguably more
|
|
correct) term "ECMAScript" in order to provide consistency with the companion
|
|
Web application technologies (JSON and AJAX) which are in common use and both
|
|
implicitly refer to JavaScript in their names.</p>
|
|
|
|
<p>Also, the terms "AJAX" and XMLHttpRequest (XHR) are used to refer to any
|
|
asynchronous browser request.</p>
|
|
|
|
<h2><a id="structure" name="structure">2 Structure of Best Practice
|
|
Statements</a></h2>
|
|
<dl>
|
|
<dt>The Heading</dt>
|
|
<dd>A summary of the functional area to be addressed by these
|
|
statements.</dd>
|
|
</dl>
|
|
<dl>
|
|
<dt>What it means</dt>
|
|
<dd>An explanation of the intention of the Best Practice statement.</dd>
|
|
</dl>
|
|
<dl>
|
|
<dt>How to do it</dt>
|
|
<dd>A discussion of the techniques and device capabilities required to
|
|
implement this Best Practice.</dd>
|
|
</dl>
|
|
<dl>
|
|
<dt>[Requires]</dt>
|
|
<dd>A summary of device capabilities required in order for this Best
|
|
Practice to apply.</dd>
|
|
</dl>
|
|
|
|
<h2><a id="bp" name="bp">3 Best Practice Statements</a></h2>
|
|
|
|
<h3><a id="bp-applicationdata" name="bp-applicationdata">3.1 Application
|
|
Data</a></h3>
|
|
|
|
<p>Most applications have the need to store data of various forms, both
|
|
intrinsic content (e.g. the emails of an email application, the calendar events
|
|
of a calendar application) and supplementary personalization settings (e.g.
|
|
preferred theme, default view, etc).</p>
|
|
|
|
<p>These Best Practices relate to the appropriate technologies and techniques
|
|
to use for managing a Web application's data.</p>
|
|
|
|
<h4><a id="bp-data-cookies" name="bp-data-cookies">3.1.1 Use Cookies
|
|
Sparingly</a></h4>
|
|
|
|
<h5><a id="d1e792" name="d1e792">3.1.1.1 What it means</a></h5>
|
|
|
|
<p>Cookies are a common and effective means to store small amounts of state on
|
|
the client. They are appropriate for simple personalization data and are
|
|
commonly used to store a token representing user identity in order to enable
|
|
automatic sign-in.</p>
|
|
|
|
<p>Information stored in cookies, however, is sent to the server for every
|
|
request and so using them for excessive amounts of data can negatively impact
|
|
performance, particularly on a mobile network.</p>
|
|
|
|
<p>Also, in the mobile context, cookie support cannot be relied upon since it
|
|
may be disabled either in the device configuration or by the mobile network.
|
|
For this reason, applications should endeavor to remain functional even if
|
|
cookies are unavailable. See <a
|
|
href="http://www.w3.org/TR/mobile-bp/#COOKIES">BP1 [COOKIES] Do not rely on
|
|
cookies being available</a> for more cookie related caveats.</p>
|
|
|
|
<h4><a id="bp-data-html5" name="bp-data-html5">3.1.2 Use Appropriate
|
|
Client-Side Storage Technologies for Local Data</a></h4>
|
|
|
|
<h5><a id="d1e818" name="d1e818">3.1.2.1 What it means</a></h5>
|
|
|
|
<p>If supported by the device, client-side storage APIs provide a mechanism to
|
|
store more extensive amounts of data than would be appropriate with cookies. At
|
|
the time of writing, work is still undergoing to unify these APIs, see the W3C
|
|
WebApps working group [<a href="#WEBAPPS">WEBAPPS</a>] and Device APIs working
|
|
group [<a href="#DAP">DAP</a>] for more information. Additionally, some
|
|
examples of existing technologies that support client-side storage APIs are
|
|
BONDI [<a href="#BONDI">BONDI</a>], HTML5 [<a href="#HTML5">HTML5</a>], and
|
|
Opera Widgets [<a href="#OPERA">OPERA</a>].</p>
|
|
|
|
<p>Making use of client-side storage in Web applications is a powerful
|
|
technique that brings Web applications into parity with native applications in
|
|
terms of start-up time and responsiveness. Two key advantages are worth noting
|
|
explicitly:</p>
|
|
<ul>
|
|
<li>Application data stored locally can be displayed immediately when the
|
|
application is started (without the need for a server roundtrip) allowing
|
|
start-up latency to be reduced.
|
|
<p></p>
|
|
</li>
|
|
<li>By making updates locally at first and replicating changes back to the
|
|
server in the background when connectivity is available, Web applications
|
|
can continue to operate responsively even when the network signal is
|
|
unreliable.</li>
|
|
</ul>
|
|
|
|
<h5><a id="d1e839" name="d1e839">3.1.2.2 How to do it</a></h5>
|
|
Each technology offers a variety of storage facilities that range from simple
|
|
"key = value" models appropriate for relatively simple, unstructured data, to
|
|
full SQL Database APIs appropriate for more extensive and structured content.
|
|
For a good technical discussion of these facilities in the context of HTML5 see
|
|
Offline Web Applications [<a href="#OFFLINE">OFFLINE</a>].
|
|
|
|
<p></p>
|
|
|
|
<p><strong>[ Client-Side Storage ]</strong> Requires: Local Storage API.</p>
|
|
</div>
|
|
|
|
<div class="head">
|
|
<h4><a id="bp-data-server" name="bp-data-server">3.1.3 Replicate Local Data</a>
|
|
To A Server If Necessary</h4>
|
|
|
|
<h5><a id="d1e870" name="d1e870">3.1.3.1 What it means</a></h5>
|
|
|
|
<p>If a client-side storage API is being used the data in it is not visible to
|
|
the user's other devices. Whilst this is appropriate for some forms of data
|
|
(e.g. preferences and state relevant only to a given device), it is often
|
|
necessary to send this data back to a server in order to provide a consistent
|
|
view across devices (e.g. between mobile and desktop instances of an
|
|
application) and make it possible to recover data if the device is lost or
|
|
damaged. See <a href="#bp-consistency">3.5.8 Ensure Consistency Of State
|
|
Between Devices</a> for further discussion on these topics.</p>
|
|
|
|
<p>As a rule of thumb, data that needs to be shared with other devices or
|
|
recovered in the case of a lost or damaged device, should be replicated back to
|
|
the server as soon as possible.</p>
|
|
|
|
<h5><a id="d1e882" name="d1e882">3.1.3.2 How to do it</a></h5>
|
|
|
|
<p>The technologies that provide client-side storage APIs provide facilities to
|
|
detect the current network connectivity. For example, HTML5 provides a property
|
|
on the navigator object (<code>navigator.onLine</code>) to
|
|
indicate whether the client is currently online, and dispatches two events on
|
|
the Window object to indicate a change of network state (<code>online</code> and <code>offline</code>).</p>
|
|
|
|
<p>However, these APIs should be used with caution. Even if the browser is
|
|
reporting an online state, on an intermittent network this is no guarantee that
|
|
a subsequent connection will succeed. The most effective approach is to fail
|
|
gracefully in the event of a connection failure, store unsaved data in a queue
|
|
of uncommitted changes, and set a timer to try again later.</p>
|
|
|
|
<p><strong>[ Client-Side Storage ]</strong> Requires: Local Storage API.</p>
|
|
|
|
<h3><a id="bp-security" name="bp-security">3.2 Security and privacy</a></h3>
|
|
|
|
<p>Use trusted information, and protect all personally identifiable
|
|
information. Mobile Web applications are subject to the same security
|
|
considerations and risks as desktop Web applications, and as such most desktop
|
|
related security advice is applicable to mobile. (For example, see OWASP [<a
|
|
href="#OWASP">OWASP</a>] for a good summary of common Web security
|
|
Best Practices). This document does not attempt to provide an exhaustive survey
|
|
of security issues but the following Best Practice has been called out on the
|
|
grounds that it is specifically relevant to mobile.</p>
|
|
|
|
<h4><a id="bp-security-json" name="bp-security-json">3.2.1 Do not Execute
|
|
Unescaped or Untrusted JSON data</a></h4>
|
|
|
|
<p><em>3.2.1.1 What it means</em></p>
|
|
|
|
<p>A common technique is to use JSON to transfer data to a client and then use
|
|
JavaScript's <code>eval()</code> function to
|
|
parse it. This is a powerful technique, since on constrained devices <code>eval()</code> can execute
|
|
more quickly than the alternatives. However, direct execution of a datafeed
|
|
that contains unescaped user-generated data represents a significant security
|
|
risk and should be avoided.</p>
|
|
|
|
<p>Inadvertently executing malicious JavaScript is particularly dangerous on
|
|
mobile devices where personal information (current location, contact data, etc)
|
|
may be exposed.</p>
|
|
|
|
<p><em>3.2.1.2 How to do it</em></p>
|
|
|
|
<p>Where possible, instead of parsing JSON data by executing it with the <code>eval()</code> function, use a JSON parser (for example a <a href="https://github.com/douglascrockford/JSON-js/raw/master/json_parse.js">JavaScript implementation of a JSON parser</a> [<a href="#JSON-PARSE">JSON-PARSE</a>]).</p>
|
|
|
|
<p>If this is impractical ensure that the data contains no user-generated
|
|
content (e.g. the server is responsible for the content of all fields in the
|
|
datafeed) or that any user-generated content is correctly escaped.</p>
|
|
|
|
<p>See RFC4627 [<a href="#RFC4627">RFC4627</a>] for details on how to ensure a JSON
|
|
datafeed is suitably escaped and can be safely passed into JavaScript's <code>eval()</code> function.</p>
|
|
|
|
<h3><a id="bp-inform-control" name="bp-inform-control">3.3 User Awareness and
|
|
Control</a></h3>
|
|
|
|
<p>Allow the user to control application behaviour that might not otherwise be
|
|
apparent, such as access to the network and access to device data. For
|
|
example:</p>
|
|
<ul>
|
|
<li>Pictures, music, and video clips;</li>
|
|
<li>Contacts, calendar (PIM data);</li>
|
|
<li>Call history;</li>
|
|
<li>System data (battery, coverage, roaming, location);</li>
|
|
<li>Media recording (record audio/video clip, get new picture);</li>
|
|
<li>Device context (e.g. location, connectivity, profile setting).</li>
|
|
</ul>
|
|
|
|
<p>Note that where possible it is preferable to rely on the browser's native
|
|
functionality to notify the user of these activities, however the Best
|
|
Practices below provide further advice on appropriate <em>application</em>
|
|
behaviour in situations where the native functionality of the browser may not
|
|
be sufficient.</p>
|
|
|
|
<h4><a id="bp-inform-personalinfo" name="bp-inform-personalinfo"
|
|
>3.3.1 Ensure the User is Informed About Use of Personal and Device
|
|
Information</a></h4>
|
|
|
|
<h5><a id="d1e656" name="d1e656">3.3.1.1 What it means</a></h5>
|
|
|
|
<p>Ensure that the user is informed if the application needs to access personal
|
|
or device information. The user should be informed of the types of information
|
|
that will be used by the application and whether / how that data will be
|
|
exchanged with the server.</p>
|
|
|
|
<p>These notices should be provided when the user first accesses the Web
|
|
application, or on first access to user information. It should provide the user
|
|
with enough information to judge whether or not they want to allow the
|
|
application access to their data.</p>
|
|
|
|
<h5><a id="d1e666" name="d1e666">3.3.1.2 How to do it</a></h5>
|
|
|
|
<p>In many cases use of APIs that provide access to personal or device
|
|
information causes a native confirmation dialog to be presented to the user. In
|
|
this case the application should not force the user to confirm again at the
|
|
application level, but should make clear in the UI that displayed data has been
|
|
accessed from the device.</p>
|
|
|
|
<p>If the user declines a prompt to allow application access to personal or
|
|
device information, the application must recover gracefully. For example, if a
|
|
request to a device API fails, do not automatically retry if this will lead to
|
|
the user being presented with repeated native confirmation dialog boxes.</p>
|
|
|
|
<p><strong>[ DEVICE DATA</strong> <strong>]</strong> Requires: Device Data
|
|
APIs.</p>
|
|
|
|
<h4><a id="bp-enable-automatic-login" name="bp-enable-automatic-login"
|
|
>3.3.2 Enable Automatic Sign-in</a></h4>
|
|
|
|
<h5><a id="bp-enable-automatic-login-what"
|
|
name="bp-enable-automatic-login-what">3.3.2.1 What it means</a></h5>
|
|
|
|
<p>If an application requires user identity it is usual to prompt for user
|
|
credentials (username and password) and provide the option to sign-in
|
|
automatically on next usage session. This is especially important on a mobile
|
|
device where data input is more difficult than on a desktop.</p>
|
|
|
|
<p>Note that if automatic sign-in is enabled, a sign-out link should also be
|
|
provided.</p>
|
|
|
|
<h5><a id="bp-enable-automatic-login-how"
|
|
name="bp-enable-automatic-login-how">3.3.2.2 How to do it</a></h5>
|
|
|
|
<p>User credentials can be stored in a cookie or in local storage. However, it
|
|
is important not to store unencrypted password information since this is
|
|
insecure. Typically, a securely hashed token which, if necessary, can be
|
|
revoked on the server, is stored locally in order to enable automatic
|
|
sign-in.</p>
|
|
|
|
<h3><a id="bp-conserve" name="bp-conserve">3.4 Conservative use of
|
|
resources</a></h3>
|
|
|
|
<p>The most effective way to ensure that applications run smoothly and with low
|
|
latency is to minimize use of device memory, processor power, and network
|
|
bandwidth which are more limited on mobile devices than on the desktop.</p>
|
|
|
|
<h4><a id="bp-conserve-compress" name="bp-conserve-compress">3.4.1 Use Transfer
|
|
Compression</a></h4>
|
|
|
|
<h5><a id="d1e687" name="d1e687">3.4.1.1 What it means</a></h5>
|
|
|
|
<p>Compress content for efficient delivery.</p>
|
|
|
|
<h5><a id="d1e693" name="d1e693">3.4.1.2 How to do it</a></h5>
|
|
|
|
<p>HTTP 1.1 compression, which uses the gzip and DEFLATE algorithms, is widely supported. Web servers should be configured to serve appropriately compressed responses.</p>
|
|
|
|
<p>Note however, that the cost (in time and battery usage) of decompressing
|
|
data should be balanced against the gains in transport efficiency. When
|
|
configuring HTTP 1.1 compression note that:</p>
|
|
<ul>
|
|
<li>Most image formats (especially JPEGs) do not benefit from compression,
|
|
but SVG does;</li>
|
|
<li>Most other media formats (e.g. audio, video) do not benefit from
|
|
compression;</li>
|
|
<li>Very small files (e.g. <1k) generally do not benefit from
|
|
compression.</li>
|
|
</ul>
|
|
|
|
<p>Where supported, alternative compression formats (such as EXI [<a href="#EXI">EXI</a>]) that do not share some of the above impediments, may provide benefit.</p>
|
|
|
|
<h4><a id="bp-conserve-contentsize" name="bp-conserve-contentsize"
|
|
>3.4.2 Minimize Application and Data Size</a></h4>
|
|
|
|
<h5><a id="d1e823" name="d1e823">3.4.2.1 What it means</a></h5>
|
|
|
|
<p>This section elaborates on the Best Practices of BP1 (<a
|
|
href="http://www.w3.org/TR/mobile-bp/#MINIMIZE">MINIMIZE</a>). Smaller
|
|
applications will download and execute more quickly and more reliably than
|
|
larger ones on constrained devices.</p>
|
|
|
|
<h5><a id="d1e832" name="d1e832">3.4.2.2 How to do it</a></h5>
|
|
|
|
<p>Process HTML, JavaScript and CSS files to remove whitespace and minify
|
|
before delivery. </p>
|
|
|
|
<p>"Minification" / "optimization" may take a number of forms from simple
|
|
removal of white space and comments, to the global substitution of tokens
|
|
(variables, method names, selector names) with shorter alternatives. In
|
|
general, minification based upon a lexical / grammatical understanding of that
|
|
source is less fragile and is preferred to simple regular-expression based
|
|
tools.</p>
|
|
|
|
<p>See <a href="http://compressorrater.thruhere.net/">the JavaScript CompressorRater</a> [<a href="#JSCOMP">JSCOMP</a>] for a comparison of JavaScript minification tools.</p>
|
|
</div>
|
|
|
|
<h4><a id="bp-redirect-minimize" name="bp-redirect-minimize">3.4.3 Avoid
|
|
Redirects</a></h4>
|
|
|
|
<h5><a id="d1e729" name="d1e729">3.4.3.1 What it means</a></h5>
|
|
|
|
<p>The redirection of requests (using HTTP 3xx status or HTML meta refresh) is
|
|
typically used to exchange information between servers (e.g. account
|
|
authentication). The delay incurred by redirects is much higher over mobile
|
|
networks and so the number of redirects should be kept to a minimum.</p>
|
|
|
|
<h5><a id="d1e736" name="d1e736">3.4.3.2 How to do it</a></h5>
|
|
|
|
<p>Try not to use redirects. If more than two redirects are required consider
|
|
using an interstitial page to communicate to the user that the application is
|
|
still working.</p>
|
|
|
|
<div class="head">
|
|
<h4><a id="bp-conserve-requests" name="bp-conserve-requests">3.4.4 Optimize
|
|
Network Requests</a></h4>
|
|
|
|
<h5><a id="d1e751" name="d1e751">3.4.4.1 What it means</a></h5>
|
|
|
|
<p>Establishing the necessary connections in order to complete an HTTP request
|
|
can take significantly longer on a mobile network than on a fixed network. Even
|
|
though bandwidth is typically more restricted on a mobile network it is still
|
|
preferable to make fewer, larger requests.</p>
|
|
|
|
<h5><a id="d1e757" name="d1e757">3.4.4.2 How to do it</a></h5>
|
|
|
|
<p>Consider the following possibilities when designing an application:</p>
|
|
<dl>
|
|
<dt><strong>Batching requests:</strong></dt>
|
|
<dd>Since a single request for more data is likely to provide a better user
|
|
experience than several smaller requests, wherever possible, batch up
|
|
multiple requests at the application level.</dd>
|
|
</dl>
|
|
<dl>
|
|
<dt><strong>Throttle low-priority requests:</strong></dt>
|
|
<dd>In some applications certain requests may be less critical than others
|
|
(e.g. logging requests). Throttle low-priority requests to ensure they
|
|
don't block the network and prevent more critical requests from being
|
|
serviced quickly.</dd>
|
|
</dl>
|
|
<dl>
|
|
<dt><strong>Back off during periods of inactivity:</strong></dt>
|
|
<dd>If the application polls for updates, it should monitor user activity
|
|
and poll less frequently during inactive periods.</dd>
|
|
</dl>
|
|
<dl>
|
|
<dt><strong>Device Context:</strong></dt>
|
|
<dd>If supported by the device, use awareness of current connectivity (e.g.
|
|
WiFi) to select an appropriate level of interaction.</dd>
|
|
</dl>
|
|
</div>
|
|
|
|
<div class="head">
|
|
<h4><a id="bp-conserve-ext-files" name="bp-conserve-ext-files"
|
|
>3.4.5 Minimize External Resources</a></h4>
|
|
|
|
<p><em>3.4.5.1 What it means</em></p>
|
|
|
|
<p>A Web application typically requires a number of resources (style sheets,
|
|
scripts, image, etc) each of which requires an HTTP request. As above, HTTP
|
|
requests are particularly expensive on a mobile network and so fewer, larger
|
|
requests should be favored over a larger number of smaller requests.</p>
|
|
|
|
<p><em>3.4.5.2 How to do it</em></p>
|
|
|
|
<p>As far as makes sense after taking into account <a
|
|
href="#bp-presentation-perceived">3.5.2 Minimize Perceived Latency</a> combine
|
|
all style sheets into a single resource and all scripts into a single resource.
|
|
If multiple scripts and style sheets are required as part of the authoring
|
|
process, then try to arrange that they are merged before the page is served.</p>
|
|
</div>
|
|
|
|
<div class="head">
|
|
<h4><a id="bp-conserve-sprites" name="bp-conserve-sprites">3.4.6 Aggregate
|
|
Static Images into a Single Composite Resource (Sprites)</a></h4>
|
|
|
|
<p><em>3.4.6.1 What it means</em></p>
|
|
|
|
<p>Web applications often depend on a number of static images to provide icons,
|
|
buttons, etc. If served as a separate image each one incurs an additional HTTP
|
|
request which is detrimental to performance.</p>
|
|
|
|
<p><em>3.4.6.2 How to do it</em></p>
|
|
|
|
<p>Define candidate images as CSS background images and combine them into a
|
|
single image for transfer (spriting). To optimize efficiency combine images of
|
|
similar sizes and color palettes. Also, combine images that do not change
|
|
often, since if one of the component images changes the entire combination
|
|
image will need to be refreshed. To render individual components of a resource
|
|
use CSS positioning and clipping.</p>
|
|
|
|
<p>Note that this technique should only be applied to <strong>decorative
|
|
</strong>images (e.g. those that don't require an <em>alt</em> text). Spriting
|
|
informational images leads to an undesirable coupling of content and layout and
|
|
is detrimental to accessibility.</p>
|
|
|
|
<p><strong>[ CSS ]</strong> Requires: CSS2 Clipping and Positioning Support</p>
|
|
|
|
<h4><a id="bp-conserve-css-images" name="bp-conserve-css-images">3.4.7 Include
|
|
Background Images Inline in CSS Style Sheets</a></h4>
|
|
|
|
<p><em>3.4.7.1 What it means</em></p>
|
|
|
|
<p>Visual effects (e.g. background images and gradients) are often used to
|
|
improve the look and feel of an application. These can be included in CSS as
|
|
base64 encoded strings in order to avoid an additional HTTP request</p>
|
|
|
|
<p>Note that base64 encoding adds around 10% to the image size after gzip
|
|
compression and this additional cost should be weighed against the benefits of
|
|
fewer requests.</p>
|
|
|
|
<p><em>3.4.7.2 How to do it</em></p>
|
|
|
|
<p>Background images can be encoded using the data URI scheme:
|
|
<code>url('data:image/png;base64, [data])</code></p>
|
|
|
|
<p><strong>[ CSS ]</strong> Requires: <a
|
|
href="http://tools.ietf.org/html/rfc2397">RFC2397</a> [<a href="#RFC2397">RFC2397</a>] data uri support.</p>
|
|
|
|
<h4><a id="bp-conserve-fingerprint" name="bp-conserve-fingerprint">3.4.8 Cache
|
|
Resources By Fingerprinting Resource References</a></h4>
|
|
|
|
<p><em>3.4.8.1. What it means</em></p>
|
|
|
|
<p>Dynamic resources that change occasionally (e.g. a user's avatar) can still
|
|
be cached by identifying them with a URI that includes a hash of the resource
|
|
content. Using this technique means that the browser does not need to check the
|
|
resource headers in order to validate its cache, instead, any change in the
|
|
resource will lead naturally to a corresponding change in the resource
|
|
reference.</p>
|
|
|
|
<p>For example, </p>
|
|
|
|
<p style="text-align:center;"><code><img
|
|
src="http://www.example.com/userimages/joeblogs-67f90da089da"></code></p>
|
|
|
|
<p>Where the actual resource at joeblogs-[xxx] could be either generated in
|
|
some offline process or served dynamically.</p>
|
|
|
|
<p><em>3.4.8.2 How to do it</em></p>
|
|
<ul>
|
|
<li>Set the resource caching policy to "never expire" by setting the
|
|
<code>Expires</code> header to a date in the far future.</li>
|
|
<li>Reference the resource using a URI that contains a Hash of the content.
|
|
If the content changes, this reference will change and the browser will
|
|
fetch the updated data.</li>
|
|
</ul>
|
|
|
|
<h4><a id="bp-conserve-ajax" name="bp-conserve-ajax">3.4.9 Cache AJAX
|
|
Data</a></h4>
|
|
|
|
<p><em>3.4.9.1 What it means</em></p>
|
|
|
|
<p>If possible, data designed to be accessed by AJAX requests from the client
|
|
should be cached in the same way as primary content.</p>
|
|
|
|
<p><em>3.4.9.2 How to do it</em></p>
|
|
|
|
<p>The standard caching techniques (<code>Expires</code> header and
|
|
<code>Cache-Control</code> header), as well as resource fingerprinting (see <a
|
|
href="#bp-conserve-fingerprint">3.4.8</a>) can be used on AJAX data as readily
|
|
as primary content pages.</p>
|
|
|
|
<h4><a id="bp-conserve-cookie" name="bp-conserve-cookie">3.4.10 Do not Send
|
|
Cookie Information Unnecessarily</a></h4>
|
|
|
|
<p><em>3.4.10.1 What it means</em></p>
|
|
|
|
<p>Static resources do not need cookie information and so performance can be
|
|
improved by serving them from a path or sub-domain for which the application's
|
|
cookies are out of scope.</p>
|
|
|
|
<p><em>3.4.10.2 How to do it</em></p>
|
|
|
|
<p>Use a different domain, sub-domain, or path name for static resources to the
|
|
main application, and restrict the valid path of cookies such that they will
|
|
not be exchanged when they are not needed.</p>
|
|
|
|
<p>For example:</p>
|
|
|
|
<div style="padding-left: 5px; border:1px solid black">
|
|
<p><code>Set-Cookie:
|
|
somePreferenceInformation=purple; path=/myapp/</code></p>
|
|
</div>
|
|
|
|
<p>Application data served from <code>/myapp</code> will receive
|
|
cookie information.</p>
|
|
|
|
<p>Static data served from <code>/static</code> will not
|
|
receive unneeded cookie information.</p>
|
|
|
|
<h4><a id="bp-conserve-dom" name="bp-conserve-dom">3.4.11 Keep DOM Size
|
|
Reasonable</a></h4>
|
|
|
|
<h5><a id="bp-conserve-dom-what" name="bp-conserve-dom-what">3.4.11.1 What it
|
|
means</a></h5>
|
|
|
|
<p>The in-memory size of the Document Object Model (DOM) may be limited on
|
|
mobile devices. Large / complex pages may exceed this limit and cause
|
|
unpredictable errors.</p>
|
|
|
|
<h5><a id="bp-conserve-dom-how" name="bp-conserve-dom-how">3.4.11.2 How to do
|
|
it</a></h5>
|
|
|
|
<p>Limit the amount of information in the DOM at a single time using pagination
|
|
or other appropriate techniques.</p>
|
|
|
|
<h3><a id="bp-presentation" name="bp-presentation">3.5 User Experience</a></h3>
|
|
|
|
<p>Given the additional complexities of interacting with an application on a
|
|
mobile device, special consideration should be given to the overall user
|
|
experience. User experience is influenced by a number of factors, including:
|
|
latency, interaction method, and data consistency.</p>
|
|
|
|
<h4><a id="bp-presentation-startup" name="bp-presentation-startup">3.5.1
|
|
Optimize For Application Start-up Time</a></h4>
|
|
|
|
<h5><a id="bp-presentation-startup-what"
|
|
name="bp-presentation-startup-what">3.5.1.1 What it means</a></h5>
|
|
|
|
<p>User experience is strongly influenced by the initial start-up time of an
|
|
application. </p>
|
|
|
|
<p>Offline Web application technologies like HTML5 AppCache [<a
|
|
href="#HTML5-OFFLINE">HTML5-OFFLINE</a>] bring Web applications into parity
|
|
with native applications in terms of their start-up time and their ability to
|
|
be used even where network coverage is intermittent. The following steps should
|
|
be considered to minimize the start time of a Web application.</p>
|
|
|
|
<h5><a id="bp-presentation-startup-how"
|
|
name="bp-presentation-startup-how">3.5.1.2 How to do it</a></h5>
|
|
|
|
<p>Consider the following techniques to help minimize application start
|
|
time:</p>
|
|
<ul>
|
|
<li><strong>Use Offline Technology:</strong> Offline Web technologies (for
|
|
example, AppCache) allow the resources of a Web application (its HTML,
|
|
JavaScript, and CSS files) to be specified and stored locally so that the
|
|
application can start without requiring a round-trip to the server.</li>
|
|
<li><strong>Consider Partitioning Large Scripts:</strong> In complex Web
|
|
applications, JavaScript parsing can contribute a significant portion of
|
|
start time. If some functionality is rarely used it should be moved into
|
|
separate scripts that can be loaded on demand, lowering the amount of core
|
|
code that needs to be parsed at start-up.</li>
|
|
<li><strong>Use Local Storage:</strong> Where appropriate, store a snapshot
|
|
of the last application state so it can be displayed immediately on
|
|
start-up without requiring a server roundtrip.</li>
|
|
<li><strong>Minimize Number of Local Storage Queries:</strong> The number of
|
|
local storage queries required to generate the initial view is a
|
|
significant contribution to start-up latency. Try to minimize the number of
|
|
local storage queries required before the first view can be displayed.</li>
|
|
</ul>
|
|
</div>
|
|
|
|
<div class="head">
|
|
<h4><a id="bp-presentation-perceived" name="bp-presentation-perceived"
|
|
>3.5.2 Minimize Perceived Latency</a></h4>
|
|
|
|
<h5><a id="bp-presentation-perceived-meaning"
|
|
name="bp-presentation-perceived-meaning">3.5.2.1 What it means</a></h5>
|
|
|
|
<p>Lowering perceived latency is an important factor in improving the overall
|
|
usability of a Web application.</p>
|
|
|
|
<h5><a id="bp-presentation-perceived-howto"
|
|
name="bp-presentation-perceived-howto">3.5.2.2 How to do it</a></h5>
|
|
|
|
<p>A number of techniques can be used to lower perceived latency:</p>
|
|
<ul>
|
|
<li><strong>Enable Incremental Rendering</strong>: Place JavaScript at the
|
|
bottom of the page (since browsers rendering halts while parsing
|
|
JavaScript) and configure the page so that any useful information that
|
|
might be available is viewable while the main content of the application is
|
|
still loading.</li>
|
|
<li><strong>Keep the User Informed of Activity:</strong> Use spinners
|
|
progress bars to keep the user informed during network and device API
|
|
accesses so that they do not think the application is halted.</li>
|
|
<li><strong>Avoid Page Reloads:</strong> To reflect changes in state or show
|
|
different views within an application, update pages dynamically (by
|
|
manipulating the DOM) rather than reloading them.</li>
|
|
<li><strong>Preload Probable Next Views:</strong> Preload data for frequently
|
|
traversed paths in the application so it can be displayed more quickly when
|
|
the user requests it.</li>
|
|
</ul>
|
|
|
|
<h4><a id="bp-presentation-interaction"
|
|
name="bp-presentation-interaction">3.5.3 Design for Multiple Interaction
|
|
Methods</a></h4>
|
|
|
|
<h5><a id="bp-presentation-interaction-what"
|
|
name="bp-presentation-interaction-what">3.5.3.1 What it means</a></h5>
|
|
|
|
<p>Interaction methods vary across devices. Three main interaction methods
|
|
should be considered when designing the UI:</p>
|
|
<ul>
|
|
<li>Focus Based: The browser focus "jumps" from element to element;</li>
|
|
<li>Pointer Based: Key-based navigation controls a pointer that can cover any
|
|
part of the screen;</li>
|
|
<li>Touch Based: Events are related directly to a finger or stylus touch
|
|
position on the screen.</li>
|
|
</ul>
|
|
|
|
<p>The optimum configuration of UI elements varies depending on the interaction
|
|
method used by the device. Ideally, the UI should be adapted based on a
|
|
knowledge of the interaction methods supported by the target device. If this is
|
|
not possible, then the UI should be designed to provide a good experience for
|
|
each of these different interaction methods.</p>
|
|
|
|
<p>Additionally note that (as always) new interaction methods are likely to
|
|
emerge in the future, particularly in the fields of voice and assistive
|
|
technology. For additional, non-mobile specific, guidelines on accessibility
|
|
and designing for assistive technologies, see Web Content Accessibility Guidelines (WCAG) 2.0 [<a href="#WCAG20">WCAG20</a>]. </p>
|
|
|
|
<h5><a id="bp-presentation-interaction-how"
|
|
name="bp-presentation-interaction-how">3.5.3.2 How to do it</a></h5>
|
|
|
|
<p>Particularly where navigation of content requires multiple links (i.e.
|
|
back/forward in a carousel) the following factors should be considered:</p>
|
|
|
|
<p><strong>Focus Based:</strong></p>
|
|
<ul>
|
|
<li>The current focus of the page is easily determined because the focus
|
|
element will be highlighted;</li>
|
|
<li>Focus area will jump automatically from one selectable element to another
|
|
(e.g. from link to link) without affecting usability even when widely
|
|
spaced.</li>
|
|
</ul>
|
|
|
|
<p><strong>Pointer Based:</strong></p>
|
|
<ul>
|
|
<li>Selectable elements that are associated with each other need to be close
|
|
as moving the pointer can be slow;</li>
|
|
<li>Selectable elements need to be large enough to be easily selected --
|
|
since the pointer often moves in steps of between 5 - 10 pixels;</li>
|
|
<li>Selectable elements should have rollovers to make it clear when the
|
|
pointer has entered their active area.</li>
|
|
</ul>
|
|
|
|
<p><strong>Touch Based:</strong></p>
|
|
<ul>
|
|
<li>Selectable elements may be (but don't have to be) widely spaced since the
|
|
user can select them directly;</li>
|
|
<li>Selectable elements must be large enough to be easily selected (e.g. list
|
|
items should have a screen height of at least around 1cm);</li>
|
|
<li>No elements are in focus until they are selected so extra information
|
|
cannot be passed to the user (e.g. rollovers will not work).</li>
|
|
</ul>
|
|
|
|
<h4><a id="bp-presentation-focus" name="bp-presentation-focus"
|
|
>3.5.4 Preserve Focus on Dynamic Page Updates</a></h4>
|
|
|
|
<h5><a id="d1e1198" name="d1e1198">3.5.4.1 What it means</a></h5>
|
|
|
|
<p>The JavaScript <code>focus</code> method can be used to move the focus to
|
|
the part of a page that has changed. However, if unexpected, this can confuse
|
|
or irritate the user, especially if returning to the previous focus is not
|
|
easy.</p>
|
|
|
|
<h5><a id="d1e1205" name="d1e1205">3.5.4.2 How to do it</a></h5>
|
|
|
|
<p>Use the JavaScript <code>focus</code> method only if it is essential to the
|
|
use of the application, and does not inhibit user control/interaction.</p>
|
|
|
|
<h4><a id="bp-presentation-fragment" name="bp-presentation-fragment">3.5.5 Use
|
|
Fragment IDs to Drive Application View</a></h4>
|
|
|
|
<p><em>3.5.5.1 What it means</em></p>
|
|
|
|
<p>Web applications can switch views without a full page reload by showing and
|
|
hiding sections of content. However, this means that the browser <back>
|
|
button doesn't work by default, and it is not possible to link directly to
|
|
specific views within an application. Usability is enhanced by enabling both of
|
|
these features:</p>
|
|
<ul>
|
|
<li>Enabling deep links (e.g. to the content of a specific email) means the
|
|
user can bookmark this view and return to it quickly;</li>
|
|
<li>Enabling the browser history provides a natural method to navigate
|
|
application views that is natively supported by the browser.</li>
|
|
</ul>
|
|
|
|
<p><em>3.5.5.2 How to do it</em></p>
|
|
|
|
<p>Assign a URI with a distinguishing fragment identifier (e.g.
|
|
<code>http://myapp.example.org/myapp#view</code>). Use JavaScript to
|
|
interrogate the browser location in order to determine which view to
|
|
display.</p>
|
|
|
|
<p>For further discussion on this topic see: <a href="http://ajaxpatterns.org/Unique_URLs">Unique URLs pattern</a> [<a href="#AJAX-UNIQUE">AJAX-UNIQUE</a>] on the Ajax Design Patterns Web site.</p>
|
|
Note that showing and hiding content in this way can have adverse affects on
|
|
accessibility if not carefully handled. See WAI-ARIA [<a href="#ARIA">ARIA</a>] for more information on writing accessible rich Web applications.
|
|
|
|
<h4><a id="bp-interaction-uri-schemes" name="bp-interaction-uri-schemes"
|
|
>3.5.6 Make Telephone Numbers "Click-to-Call"</a></h4>
|
|
|
|
<h5><a id="d1e1257" name="d1e1257">3.5.6.1 What it means</a></h5>
|
|
|
|
<p>Standardized URI schemes have been defined for some common device functions,
|
|
e.g. making phone calls, sending an SMS, and managing address books. These URI
|
|
schemes, if supported, can enable users to easily use these functions from Web
|
|
applications.</p>
|
|
|
|
<h5><a id="d1e1263" name="d1e1263">3.5.6.2 How to do it</a></h5>
|
|
|
|
<p>The most broadly supported scheme is tel: as described in RFC3966 [<a href="#RFC3966">RFC3966</a>]. Code such as the following can be used to enable
|
|
"Click-to-Call":</p>
|
|
|
|
<p style="text-align:center;"><code><a
|
|
href="tel:[PHONE-NUMBER]">[PHONE-NUMBER]</a></code></p>
|
|
|
|
<p>Note that [PHONE-NUMBER] should always be entered using the full
|
|
international prefix (e.g. +1-201-555-0111) to ensure that it works outside of
|
|
its home country.</p>
|
|
|
|
<p>Similarly RFC5724 [<a href="#RFC5724">RFC5724</a>] can be used to send a GSM SMS (text message) as follows:</p>
|
|
|
|
<p style="text-align:center;"><code><a
|
|
href="sms:[PHONE-NUMBER]?body=[MESSAGE]">[PHONE-NUMBER]</a></code></p>
|
|
|
|
<p>Note that at the time of writing support for this RFC is limited and device
|
|
compatibility should be verified before deployment.</p>
|
|
|
|
<h4><a id="bp-presentation-flow" name="bp-presentation-flow">3.5.7 Ensure
|
|
Paragraph Text Flows</a></h4>
|
|
|
|
<p><em>3.5.7.1 What it means</em></p>
|
|
|
|
<p>On small screens it is important that paragraph text flows both so that it
|
|
doesn't require horizontal scrolling and so that it will re-flow if the view
|
|
orientation is changed. See <a href="http://www.w3.org/TR/mobile-bp/#MEASURES"
|
|
>BP1 [MEASURES]</a> for more details.</p>
|
|
|
|
<p><em>3.5.7.2 How to do it</em></p>
|
|
|
|
<p>Do not use absolute or pixel measures. Use percentage and RELATIVE measures
|
|
for containers so that text can re-flow automatically.</p>
|
|
|
|
<h4><a id="bp-consistency" name="bp-consistency">3.5.8 Ensure Consistency Of
|
|
State Between Devices</a></h4>
|
|
|
|
<p><em>3.5.8.1 What it means</em></p>
|
|
|
|
<p>This recommendation builds on the recommendation in BP1 (<a
|
|
href="http://www.w3.org/TR/mobile-bp/#tc">5.5.1 Thematic Consistency</a>) and
|
|
expands it to consider the <em>application preferences</em>,
|
|
<em>personalization data</em>, and <em>state</em> that form part of the overall
|
|
experience on a mobile Web application.</p>
|
|
|
|
<p>User credentials valid on one device should be valid on other devices. User
|
|
preferences captured on one device should be accessible on other devices. Data
|
|
updated on one device should be viewable consistently on other devices.</p>
|
|
|
|
<p>An important example of this is offering a consistent experience where data
|
|
entered on a desktop is available on a mobile and vice versa.</p>
|
|
|
|
<p><em>3.5.8.2 How to do it</em></p>
|
|
|
|
<p>For any application data that is not exclusively relevant to the current
|
|
device, favor storing it on the server so it can be shared by other devices.
|
|
See <a href="#bp-applicationdata">3.1 Application Data</a> for more details.</p>
|
|
|
|
<div class="head">
|
|
<h4><a id="bp-conserve-usepush" name="bp-conserve-usepush">3.5.9 Consider
|
|
Mobile Specific Technologies for Initiating Web Applications</a></h4>
|
|
|
|
<h5><a id="d1e7921" name="d1e7921">3.5.9.1 What it means</a></h5>
|
|
|
|
<p>Network-initiated content delivery ("push") methods allow notifications and
|
|
updates to be sent to the user even when they are outside of the application
|
|
context.</p>
|
|
|
|
<h5><a id="d1e798" name="d1e798">3.5.9.2 How to do it</a></h5>
|
|
|
|
<p>Push method support may be disclosed through a User Agent Profile [<a href="#UAPROF">UAPROF</a>] document if published by the device vendor, or through a device classification repository.</p>
|
|
|
|
<p>If supported by the user agent, options for Push methods include:</p>
|
|
<ul>
|
|
<li>OMA Push: a widely supported enabler providing methods for user-confirmed and automatic content push, directed to mobile browsers and other user-agents. See <a href="http://www.openmobilealliance.org/Technical/wapindex.aspx">OMA Push specifications</a> [<a href="#OMA-PUSH">OMA-PUSH</a>] for more details;</li>
|
|
<li>SMS;</li>
|
|
<li>QR Codes;</li>
|
|
<li>Alternative vendor-specific initiatives.</li>
|
|
</ul>
|
|
|
|
<h4><a id="bp-viewport" name="bp-viewport">3.5.10 Use Meta Viewport Element To
|
|
Identify Desired Screen Size</a></h4>
|
|
|
|
<h5><a id="d1e1944" name="d1e1944">3.5.10.1 What it means</a></h5>
|
|
|
|
<p>Certain classes of browser attempt to display desktop pages on a small
|
|
screen by automatically zooming the display. This can be problematic for
|
|
applications that have already been optimized for a small screen. The viewport
|
|
meta tag tells the device at what scale to render the page.</p>
|
|
|
|
<h5><a id="d1e1951" name="d1e1951">3.5.10.2 How to do it</a></h5>
|
|
|
|
<p>A typical viewport setting looks like this:</p>
|
|
|
|
<p style="text-align:center;"><code><meta name="viewport"
|
|
content="width=device-width, initial-scale=1.0"/></code> ,</p>
|
|
|
|
<p>and is inserted into the <code><head></code> element
|
|
of the HTML document. This setting informs the browser to always render the
|
|
page at 100% (e.g. no browser based scaling) and is appropriate for pages
|
|
specifically designed for the target screen-size.</p>
|
|
</div>
|
|
|
|
<h3><a id="bp-devcap" name="bp-devcap">3.6 Handling Variation in the Delivery
|
|
Context</a></h3>
|
|
|
|
<p>Variations in the Delivery Context (such as different device capabilities)
|
|
is a prominent feature of the mobile Web. Web applications should adapt to
|
|
known or discoverable properties of the Delivery Context by adjusting the
|
|
content, navigation or page flow, with a view to offering a good user
|
|
experience on as broad a range of devices as possible.</p>
|
|
|
|
<h4><a id="bp-devcap-detection" name="bp-devcap-detection">3.6.1 Prefer
|
|
Server-Side Detection Where Possible</a></h4>
|
|
|
|
<h5><a id="d1e1397" name="d1e1397">3.6.1.1 What it means</a></h5>
|
|
|
|
<p>Where possible, use the evidence available on the server to determine the
|
|
properties of the Delivery Context, and adapt the responses to the client
|
|
before transfer, thus improving the user experience and avoiding transfer of
|
|
unnecessary or incompatible data.</p>
|
|
|
|
<h5><a id="d1e1403" name="d1e1403">3.6.1.2 How to do it</a></h5>
|
|
|
|
<p>In its most basic form, the minimum evidence from the requesting device is
|
|
the HTTP request header fields. Typically, the following header fields provide
|
|
evidence of device capabilities: </p>
|
|
<ul>
|
|
<li><strong>Accept:</strong> this list of MIME types can aid in the selection
|
|
or creation of alternative content representations to suit the requesting
|
|
device. This field is not always reliable however, and its value often
|
|
includes "*/*", suggesting that clients can accept every MIME type.</li>
|
|
<li><strong>User-Agent:</strong> as a generally unique (albeit opaque) string
|
|
it can be used as a key into a device description repository [<a
|
|
href="#DDR">DDR</a>]. The set of properties recorded in these repositories
|
|
varies from implementation to implementation. The W3C DDR Simple API
|
|
defines a common interface and a means of expressing the vocabulary of
|
|
properties for such repositories.</li>
|
|
<li><strong>X-Wap-Profile:</strong> this is a reference to the User Agent
|
|
Profile [<a href="#UAPROF">UAPROF</a>] for the requesting device. In
|
|
practice, the referenced profile is not always guaranteed to be available,
|
|
valid or up-to-date, so the value of this field is sometimes used with a
|
|
DDR where corrections to the profiles are stored. Some devices may send an
|
|
additional field <strong>X-Wap-Profile-Diff</strong> advertising temporary
|
|
or permanent variations of a specific device with respect to its standard
|
|
profile.</li>
|
|
</ul>
|
|
|
|
<h4><a id="bp-devcap-scripting" name="bp-devcap-scripting">3.6.2 Use
|
|
Client-Side Capability Detection Where Necessary</a></h4>
|
|
|
|
<h5><a id="d1e1422" name="d1e1422">3.6.2.1 What it means</a></h5>
|
|
|
|
<p>Where it is not possible to determine certain properties of the Delivery
|
|
Context from the server, this information may be available at the client. Once
|
|
obtained at the client, the information can be used directly to adapt the
|
|
presentation, or it can used to request alternative, adapted content from the
|
|
server.</p>
|
|
|
|
<h5><a id="d1e1428" name="d1e1428">3.6.2.2 How to do it</a></h5>
|
|
|
|
<p>There are a few client-side solutions available to the developer:</p>
|
|
|
|
<p style="margin-left:2em;"><strong>JavaScript:</strong> this is the most
|
|
common solution. A script determines the device / browser properties and
|
|
manipulates the content and behaviour of the application accordingly. This can
|
|
be done in two ways:</p>
|
|
<ol>
|
|
<li style="margin-left:4em">By encapsulating the differing
|
|
behaviors in the control logic of the application (e.g. <code>if (some_api_exists) {
|
|
...</code>). Typically the Delivery Context information is gathered at the
|
|
start of the session, though dynamic information (e.g. current screen
|
|
orientation) should be refreshed during the session.</li>
|
|
<li style="margin-left:4em">By passing the gathered information back to the
|
|
server and requesting alternative content (e.g. either by dynamically
|
|
adding a new <code><script></code>
|
|
element to the DOM or by an XHR request). </li>
|
|
</ol>
|
|
|
|
<p style="margin-left:2em;"><strong>CSS Media Types:</strong> CSS Media Types
|
|
allow different stylesheets to be associated with different media types (e.g.
|
|
print, screen, mobile) and are traditionally used to repurpose content for
|
|
these destinations. Since the list of recognized media types is limited,
|
|
however, and devices are notoriously idiosyncratic in their interpretation of
|
|
types, it is in general not a helpful technology in this context. See Media
|
|
Types [<a href="#CSSMT">CSSMT</a>] for more details.</p>
|
|
|
|
<p style="margin-left:2em;"><strong>CSS Media Queries:</strong> Media queries
|
|
are an extension to the "media-types" paradigm that allow developers to apply
|
|
specific style rules based on the device display characteristics (e.g. screen
|
|
width, orientation, or resolution). At the time of writing this specification
|
|
is not fully supported, but can provide a useful way to modify the page layout
|
|
(for example to re-flow sections of text) in a more maintainable, declarative
|
|
way than is possible with script. See Media Queries [<a
|
|
href="#CSSMQ">CSSMQ</a>] for more details. </p>
|
|
|
|
<h4><a id="bp-devcap-classify" name="bp-devcap-classify">3.6.3 Use Device
|
|
Classification to Simplify Content Adaptation</a></h4>
|
|
|
|
<h5><a id="d1e1451" name="d1e1451">3.6.3.1 What it means</a></h5>
|
|
|
|
<p>If a large number of devices are being targeted, or if the application is
|
|
sensitive to the permutations of a large number of configuration properties,
|
|
the number of application variants required might quickly become
|
|
unmanageable.</p>
|
|
|
|
<p>To combat this, classify target devices and build a single application
|
|
variant for each class. This allows you to exploit device capabilities with a
|
|
manageable code base.</p>
|
|
|
|
<h5><a id="d1e1464" name="d1e1464">3.6.3.2 How to do it</a></h5>
|
|
|
|
<p>Identify the target devices for the application and assign these to device
|
|
classes of varying capability. Focus on application variants that work in each
|
|
class rather than building device-specific exceptions for every variation in
|
|
device configuration.</p>
|
|
|
|
<p>Device classes should be defined on an application by application basis, so
|
|
that the variants can be tailored accordingly. </p>
|
|
|
|
<p>Example 1: Possible definition of application classes based on rendering and
|
|
device API capabilities:</p>
|
|
|
|
<p style="margin-left:2em;"><strong>Class 1:</strong> Basic XHTML support, no
|
|
or very basic scripting. No XHR support. (Even if these kind of devices are not
|
|
being explicitly supported, it is often advisable to support a non-XHR version
|
|
in case JavaScript has been disabled on the device).</p>
|
|
|
|
<p style="margin-left:2em;"><strong>Class 2:</strong> Full AJAX and JavaScript
|
|
support.</p>
|
|
|
|
<p style="margin-left:2em;"><strong>Class 3:</strong> Advanced device APIs, for
|
|
example: access to location API, device PIM data, or application cache.</p>
|
|
|
|
<p>Example 2: Possible definition of application classes based on supported
|
|
user-interaction modes:</p>
|
|
|
|
<p style="margin-left:2em;"><strong>Class 1:</strong> Pointer Based.</p>
|
|
|
|
<p style="margin-left:2em;"><strong>Class 2:</strong> Touch Based.</p>
|
|
|
|
<h4><a id="bp-devcap-scripting-support" name="bp-devcap-scripting-support"
|
|
>3.6.4 Support a non-JavaScript Variant if Appropriate</a></h4>
|
|
|
|
<h5><a id="d1e1493" name="d1e1493">3.6.4.1 What it means</a></h5>
|
|
|
|
<p>Scripted and XHR based applications are not supported on all browsers. If
|
|
broadest reach is a primary concern then consider providing a variant of the
|
|
application that uses synchronous FORM posts in place of XHR requests. This
|
|
Best Practice is related (albeit with a differing focus) to <a
|
|
href="http://www.w3.org/TR/mobile-bp/#OBJECTS_OR_SCRIPT">BP 1 [
|
|
OBJECTS_OR_SCRIPT]</a>.</p>
|
|
|
|
<h5><a id="d1e1499" name="d1e1499">3.6.4.2 How to do it</a></h5>
|
|
|
|
<p>Essentially this BP states that it is favorable to support "Class 1" devices
|
|
as defined in the first example above if appropriate. Doing this will ensure
|
|
that the application can be used across as broad a range of devices as
|
|
possible. Furthermore, in some cases a non-JavaScript version can be useful for
|
|
simple operations in low-bandwidth situations.</p>
|
|
|
|
<p>In some cases, however, a particular application simply has no
|
|
non-JavaScript counterpart (e.g. a Web based game, an Instant Messaging client)
|
|
in which case the server should return a response with human readable content
|
|
explaining the situation in more detail.</p>
|
|
|
|
<p>Ideally, content should be adapted before transfer by checking whether or
|
|
not the device supports JavaScript using a DDR or local index. However, in some
|
|
cases (e.g. if the device has disabled JavaScript) JavaScript may still be sent
|
|
to a device that can't process it. To cover this case, a <code><noscript></code>
|
|
element should always be included and contain a suitably informative
|
|
message.</p>
|
|
|
|
<h4><a id="bp-devcap-user-choice" name="bp-devcap-user-choice">3.6.5 Offer
|
|
Users a Choice of Interfaces</a></h4>
|
|
|
|
<h5><a id="d1e15151" name="d1e15151">3.6.5.1 What it means</a></h5>
|
|
|
|
<p>Not only is device characteristic detection imperfect, it cannot always
|
|
account for the differing use cases of an application. Therefore automatic
|
|
detection is not sufficient as the only mechanism for determining which version
|
|
is appropriate.</p>
|
|
|
|
<h5><a id="d1e15152" name="d1e15152">3.6.5.2 How to do it</a></h5>
|
|
|
|
<p>Where multiple versions of an application exist (e.g. to support the various
|
|
device classifications) always offer the user the opportunity to change the
|
|
selection.</p>
|
|
|
|
<p>Always attempt to default to the most appropriate UI on first use.</p>
|
|
|
|
<p>Always remember the user's preference for future visits in a cookie or local
|
|
data store.</p>
|
|
|
|
<h3><a id="bp-further" name="bp-further">3.7 Further Considerations</a></h3>
|
|
|
|
<p>The Mobile Web Best Practices Working Group would like to draw the attention
|
|
of Web application developers on the following considerations. These
|
|
considerations should not be viewed as best practices, because they are not
|
|
prevalent in the development community at the time of writing. They are
|
|
published as advisory notes.</p>
|
|
|
|
<h4><a id="bp-canvas" name="bp-canvas">3.7.1 Consider Use of Canvas Element or
|
|
SVG For Dynamic Graphics</a></h4>
|
|
|
|
<h5><a id="bp-canvas-meaning" name="bp-canvas-meaning">3.7.1.1 What it
|
|
means</a></h5>
|
|
|
|
<p>Canvas and SVG provide alternative options for incorporating graphics in a
|
|
Web application. Support for these technologies varies across devices so in
|
|
many cases the choice of which technology to use will depend on the target
|
|
devices for a given application.</p>
|
|
|
|
<p>The canvas element specifies a display region where JavaScript can be used
|
|
to draw simple graphics. In contrast, SVG is an XML language for defining
|
|
vector graphic elements that are added to a DOM which can be modified using
|
|
JavaScript.</p>
|
|
|
|
<p>SVG is well-suited for graphics that must be scalable and whose components
|
|
need to be modified (e.g. panning and zooming a map) whereas canvas is better
|
|
suited where a static bitmap is sufficient (e.g. drawing a scatter-chart or
|
|
creating visual effects).</p>
|
|
|
|
<p>If speed is important, canvas may be more effective. However since Canvas
|
|
generates a flat bitmap it is not inherently accessible and so should not be
|
|
used as the sole means of conveying information.</p>
|
|
|
|
<h5><a id="bp-canvas-how" name="bp-canvas-how">3.7.1.2 How to do it</a></h5>
|
|
|
|
<p>See <a href="http://www.w3.org/TR/html5/the-canvas-element.html#the-canvas-element">the Canvas Element in the HTML5 specification</a> [<a href="#HTML5">HTML5</a>, section 4.8.10] for information on how to use the Canvas element.</p>
|
|
|
|
<p>See <a href="http://www.w3.org/Graphics/SVG/">W3C Scalable Vector Graphics (SVG) home page</a> [<a href="#SVG">SVG</a>] for information on how to use SVG.</p>
|
|
|
|
<h4><a id="bp-inform-automation" name="bp-inform-automation">3.7.2 Inform the
|
|
User About Automatic Network Access</a></h4>
|
|
|
|
<h5><a id="d1e607" name="d1e607">3.7.2.1 What it means</a></h5>
|
|
|
|
<p>Network traffic on a mobile device depletes the battery and may incur
|
|
expense -- so it is important to inform the user when accessing the network.
|
|
Whenever an application makes asynchronous XHR data requests, whether in
|
|
response to a user action or automatically, this should be indicated in an
|
|
appropriate manner so that the user remains informed and in control.</p>
|
|
|
|
<h5><a id="d1e613" name="d1e613">3.7.2.2 How to do it</a></h5>
|
|
|
|
<p>Applications should disclose how they use network resources. A simple icon
|
|
indicating background activity is usually sufficient and does not interrupt the
|
|
flow of the application. If extensive background network activity is required
|
|
the user should be informed when they first visit the site, when they first
|
|
sign-in, or in associated help pages.</p>
|
|
|
|
<p>The kinds of detailed information that could be disclosed in associated help
|
|
pages or terms of service are:</p>
|
|
<ul>
|
|
<li>how often the application will interact with the Internet - e.g. every 5
|
|
minutes, hourly, daily;</li>
|
|
<li>for how long the automatic behavior will continue;</li>
|
|
<li>how heavy the overall usage is expected to be or the type of service plan
|
|
recommended.</li>
|
|
</ul>
|
|
|
|
<h4><a id="bp-inform-network" name="bp-inform-network">3.7.3 Provide Sufficient
|
|
Means to Control Automatic Network Access</a></h4>
|
|
|
|
<h5><a id="d1e6311" name="d1e6311">3.7.3.1 What it means</a></h5>
|
|
|
|
<p>If an application makes automatic network requests (e.g. to poll the server
|
|
for updates or to automatically store an updated client state) a means to
|
|
control this activity should be provided.</p>
|
|
|
|
<h5><a id="d1e6312" name="d1e6312">3.7.3.2 How to do it</a></h5>
|
|
|
|
<p>All applications that access the network automatically should provide a
|
|
means for the user to disable that activity. When automatic network activity is
|
|
disabled, periodically prompt the user to make network requests.</p>
|
|
|
|
<p>Consider allowing the user to adjust the polling schedule and to control
|
|
which activities are allowed to initiate network requests.</p>
|
|
|
|
<h2><a id="dependent-properties" name="dependent-properties"
|
|
>Appendix 1: Best Practice Dependent Device Properties</a></h2>
|
|
|
|
<p>The following device properties included in the DDR Core Vocabulary [<a
|
|
href="#DDR-VOCAB">DDR-VOCAB</a>] are of particular value in supporting best
|
|
practices recommended in this document. They should be available in any DDR
|
|
supporting the W3C's DDR Core Vocabulary:</p>
|
|
<ul>
|
|
<li>Display Width, Display Height, Display Color Depth</li>
|
|
<li>Input Devices</li>
|
|
<li>Markup Support</li>
|
|
<li>Stylesheet Support</li>
|
|
<li>Image Format Support</li>
|
|
<li>Input Mode Support</li>
|
|
<li>Cookie Support</li>
|
|
<li>Script Support</li>
|
|
</ul>
|
|
|
|
<h2><a id="references" name="references">Appendix 2: References</a></h2>
|
|
|
|
<h3><a id="ref-mwi" name="ref-mwi">2.1 MWI References</a></h3>
|
|
|
|
<p><strong><a name="MWBP" id="MWBP">MWBP</a></strong></p>
|
|
|
|
<p style="margin-left:2em;">Mobile Web Best Practices 1.0, Jo Rabin, Editor,
|
|
W3C Recommendation, 29 July 2008 (see <a
|
|
href="http://www.w3.org/TR/mobile-bp/">http://www.w3.org/TR/mobile-bp/</a>) </p>
|
|
|
|
<h3><a id="ref-dip" name="ref-dip">2.2 Device Independence</a></h3>
|
|
<dl>
|
|
<dt class="label"><a name="DCODI" id="DCODI">DCODI</a></dt>
|
|
<dd>Delivery Context Overview for Device Independence, , R. Gimson, R.
|
|
Lewis, S. Sathish, Editors, W3C Working Group Note, 20 March 2006 (See <a
|
|
href="http://www.w3.org/TR/di-dco/">http://www.w3.org/TR/di-dco/</a>)</dd>
|
|
<dt class="label"><a name="DIGLOSS" id="DIGLOSS">DIGLOSS</a></dt>
|
|
<dd>Glossary of Terms for Device Independence, R. Lewis, Editor, W3C
|
|
Working Draft (work in progress), 18 January 2005 (See <a
|
|
href="http://www.w3.org/TR/2005/WD-di-gloss-20050118/">http://www.w3.org/TR/2005/WD-di-gloss-20050118/</a>)</dd>
|
|
<dt class="label"><a name="DIP" id="DIP">DIP</a></dt>
|
|
<dd>Device Independence Principles, R. Gimson, Editor, W3C Working Group
|
|
Note, 1 September 2003 (See <a
|
|
href="http://www.w3.org/TR/2003/NOTE-di-princ-20030901/">http://www.w3.org/TR/2003/NOTE-di-princ-20030901/</a>)</dd>
|
|
</dl>
|
|
|
|
<h3><a id="ref-web" name="ref-web">2.3 Web, Protocols and Languages</a></h3>
|
|
<dl>
|
|
<dt class="label"><a name="CSS" id="CSS">CSS</a></dt>
|
|
<dd>Cascading Style Sheets (CSS1) Level 1 Specification, Håkon Wium Lie,
|
|
Bert Bos, Editors, W3C Recommendation, 11 January 1999, revised 11 April
|
|
2008 (See <a
|
|
href="http://www.w3.org/TR/2008/REC-CSS1-20080411/">http://www.w3.org/TR/2008/REC-CSS1-20080411/</a>)</dd>
|
|
<dt class="label"><a name="CSS2" id="CSS2">CSS2</a></dt>
|
|
<dd>Cascading Style Sheets, level 2 CSS2 Specification, Bert Bos, Håkon
|
|
Wium Lie, Chris Lilley, Ian Jacobs, Editors, W3C Recommendation, 12 May
|
|
1998, revised 11 April 2008 (See <a
|
|
href="http://www.w3.org/TR/2008/REC-CSS2-20080411/">http://www.w3.org/TR/2008/REC-CSS2-20080411/</a>)</dd>
|
|
<dt class="label"><a name="HTTP1.0" id="HTTP1.0">HTTP1.0</a></dt>
|
|
<dd>Hypertext Transfer Protocol -- HTTP/1.0 Request for Comments: 1945, T.
|
|
Berners-Lee, R. Fielding, H. Frystyk, May 1996 (See <a
|
|
href="http://www.w3.org/Protocols/rfc1945/rfc1945">http://www.w3.org/Protocols/rfc1945/rfc1945</a>)</dd>
|
|
<dt class="label"><a name="HTTP1.1" id="HTTP1.1">HTTP1.1</a></dt>
|
|
<dd>Hypertext Transfer Protocol -- HTTP/1.1 Request for Comments: 2616, R.
|
|
Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P. Leach, T.
|
|
Berners-Lee, June 1999 (See <a
|
|
href="http://www.w3.org/Protocols/rfc2616/rfc2616.html">http://www.w3.org/Protocols/rfc2616/rfc2616.html</a>)</dd>
|
|
<dt class="label"><a name="XML" id="XML">XML</a></dt>
|
|
<dd>Extensible Markup Language (XML) 1.0 (Fifth Edition), Tim Bray, Jean
|
|
Paoli, C. M. Sperberg-McQueen, Eve Maler, François Yergeau, Editors, W3C
|
|
Recommendation, 26 November 2008 (See <a
|
|
href="http://www.w3.org/TR/2008/REC-xml-20081126/">http://www.w3.org/TR/2008/REC-xml-20081126/</a>)</dd>
|
|
</dl>
|
|
|
|
<h3><a id="ref-other" name="ref-other">2.4 Other References</a></h3>
|
|
<dl>
|
|
<dt class="label"><a name="AJAX-UNIQUE" id="AJAX-UNIQUE">AJAX-UNIQUE</a></dt>
|
|
<dd>Unique URLs pattern on Ajax Design Patterns Web site (See <a href="http://ajaxpatterns.org/Unique_URLs">http://ajaxpatterns.org/Unique_URLs</a>)</dd>
|
|
|
|
<dt class="label"><a name="ARIA" id="ARIA">ARIA</a></dt>
|
|
<dd>Accessible Rich Internet Applications (WAI-ARIA) 1.0, James Craig et
|
|
al, W3C Working Draft, 16 September 2010 (See <a
|
|
href="http://www.w3.org/TR/wai-aria/">http://www.w3.org/TR/wai-aria/</a>)</dd>
|
|
<dt class="label"><a name="BONDI" id="BONDI">BONDI</a></dt>
|
|
<dd>OMTP Reference Implementation (see <a
|
|
href="http://bondi.omtp.org/">http://bondi.omtp.org/</a>)</dd>
|
|
<dt class="label"><a name="CSSMQ" id="CSSMQ">CSSMQ</a></dt>
|
|
<dd>Media Queries, Håkon Wium Lie, Tantek elik, Daniel Glazman, Anne van
|
|
Kesteren, W3C Candidate Recommendation, 27 July 2010 (see <a
|
|
href="http://www.w3.org/TR/css3-mediaqueries/">http://www.w3.org/TR/css3-mediaqueries/</a>)</dd>
|
|
<dt class="label"><a name="CSSMT" id="CSSMT">CSSMT</a></dt>
|
|
<dd>Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification, Bert
|
|
Bos et al, W3C Candidate Recommendation, 08 September 2009 (see <a
|
|
href="http://www.w3.org/TR/CSS21/media.html">http://www.w3.org/TR/CSS21/media.html</a>)</dd>
|
|
<dt class="label"><a name="DAP" id="DAP">DAP</a></dt>
|
|
<dd>W3C Device APIs Working Group (see <a
|
|
href="http://www.w3.org/2009/dap/">http://www.w3.org/2009/dap/</a>)</dd>
|
|
<dt class="label"><a name="DDR" id="DDR">DDR</a></dt>
|
|
<dd>Device Description Repository Simple API, Jo Rabin et al, W3C
|
|
Recommendation, 05 December 2008 (see <a
|
|
href="http://www.w3.org/TR/DDR-Simple-API/">http://www.w3.org/TR/DDR-Simple-API/</a>)</dd>
|
|
<dt class="label"><a name="DDR-VOCAB" id="DDR-VOCAB">DDR-VOCAB</a></dt>
|
|
<dd>Device Description Repository Core Vocabulary, Jo Rabin et al, W3C
|
|
Working Group Note, 14 April 2008 (see <a
|
|
href="http://www.w3.org/TR/ddr-core-vocabulary/">http://www.w3.org/TR/ddr-core-vocabulary/</a>)</dd>
|
|
<dt class="label"><a name="EXI" id="EXI">EXI</a></dt>
|
|
<dd>Efficient XML Interchange, W3C Candidate Recommendation, John Schneider
|
|
and Takuki Kamiya, 08 December 2009 (see <a
|
|
href="http://www.w3.org/TR/exi/">http://www.w3.org/TR/exi/</a>)</dd>
|
|
<dt class="label"><a name="HTML5" id="HTML5">HTML5</a></dt>
|
|
<dd>HTML5, Ian Hickson and David Hyatt, W3C Working Draft, 19 October 2010
|
|
(see <a
|
|
href="http://www.w3.org/TR/html5/">http://www.w3.org/TR/html5/</a>)</dd>
|
|
<dt class="label"><a name="HTML5-OFFLINE"
|
|
id="HTML5-OFFLINE">HTML5-OFFLINE</a></dt>
|
|
<dd>HTML5, Ian Hickson and David Hyatt, W3C Working Draft, 19 October 2010
|
|
(see <a
|
|
href="http://www.w3.org/TR/html5/offline.html#offline">http://www.w3.org/TR/html5/offline.html#offline</a>)</dd>
|
|
|
|
<dt class="label"><a name="JSCOMP" id="JSCOMP">JSCOMP</a></dt>
|
|
<dd>The JavaScript CompressorRater (see <a href="http://compressorrater.thruhere.net">http://compressorrater.thruhere.net</a>)</dd>
|
|
|
|
<dt class="label"><a name="JSON-PARSE" id="JSON-PARSE">JSON-PARSE</a></dt>
|
|
<dd>Implementation of a secure JSON parser in JavaScript (see <a href="https://github.com/douglascrockford/JSON-js/raw/master/json_parse.js">https://github.com/douglascrockford/JSON-js/raw/master/json_parse.js</a>)</dd>
|
|
|
|
<dt class="label"><a name="OFFLINE" id="OFFLINE">OFFLINE</a></dt>
|
|
<dd>Offline Web Applications, Anne Van Kesteren and Ian Hickson, W3C
|
|
Working Group Note, 30 May 2008 (see <a
|
|
href="http://www.w3.org/TR/offline-webapps/">http://www.w3.org/TR/offline-webapps/</a>)</dd>
|
|
|
|
<dt class="label"><a name="OMA-PUSH" id="OMA-PUSH">OMA-PUSH</a></dt>
|
|
<dd>OMA Push (see <a href="http://www.openmobilealliance.org/Technical/wapindex.aspx">http://www.openmobilealliance.org/Technical/wapindex.aspx</a>)</dd>
|
|
|
|
<dt class="label"><a name="OPERA" id="OPERA">OPERA</a></dt>
|
|
<dd>Opera Web Widget API (see <a
|
|
href="http://dev.opera.com/libraries/widgetobject/">http://dev.opera.com/libraries/widgetobject/</a>)</dd>
|
|
<dt class="label"><a name="OWASP" id="OWASP">OWASP</a></dt>
|
|
<dd>Open Web Application Security Project (see <a
|
|
href="http://www.owasp.org/index.php/Main_Page">http://www.owasp.org/index.php/Main_Page</a>)</dd>
|
|
|
|
<dt class="label"><a name="RFC2397" id="RFC2397">RFC2397</a></dt>
|
|
<dd>The "data" URL scheme, L.Masinter. IETF, August 1998
|
|
(See <a href="http://www.ietf.org/rfc/rfc2397.txt">http://www.ietf.org/rfc/rfc2397.txt</a>)</dd>
|
|
|
|
<dt class="label"><a name="RFC3966" id="RFC3966">RFC3966</a></dt>
|
|
<dd>The tel URI for Telephone Numbers, H. Schulzrinne. IETF, December 2004
|
|
(See <a
|
|
href="http://www.ietf.org/rfc/rfc3966.txt">http://www.ietf.org/rfc/rfc3966.txt</a>)</dd>
|
|
|
|
<dt class="label"><a name="RFC4627" id="RFC4627">RFC4627</a></dt>
|
|
<dd>The application/json Media Type for JavaScript Object Notation (JSON),
|
|
D. Crockford, July 2006 (see <a
|
|
href="http://www.ietf.org/rfc/rfc4627">http://www.ietf.org/rfc/rfc4627</a>)</dd>
|
|
<dt class="label"><a name="RFC5724" id="RFC5724">RFC5724</a></dt>
|
|
<dd>URI Scheme for Global System for Mobile Communications (GSM) Short
|
|
Message Service (SMS), E. Wilde and A. Vaha-Sipila. IETF, January 2010
|
|
(See <a
|
|
href="http://www.ietf.org/rfc/rfc5724.txt">http://www.ietf.org/rfc/rfc5724.txt</a>)</dd>
|
|
|
|
<dt class="label"><a name="SVG" id="SVG">SVG</a></dt>
|
|
<dd>W3C Scalable Vector Graphics (SVG) home page (see <a href="http://www.w3.org/Graphics/SVG/">http://www.w3.org/Graphics/SVG/</a>)</dd>
|
|
|
|
<dt class="label"><a name="UAPROF" id="UAPROF">UAPROF</a></dt>
|
|
<dd>Open Mobile Alliance OMA-TS-UAProf-V2_0-20060206-A User Agent Profile
|
|
Approved Version 2.0 06 Feb 2006 (See <a
|
|
href="http://www.openmobilealliance.org/technical/release_program/docs/UAProf/V2_0-20060206-A/OMA-TS-UAProf-V2_0-20060206-A.pdf">http://www.openmobilealliance.org/technical/release_program/docs/UAProf/V2_0-20060206-A/OMA-TS-UAProf-V2_0-20060206-A.pdf</a>)</dd>
|
|
<dt class="label"><a name="WCAG20" id="WCAG20">WCAG20</a></dt>
|
|
<dd>Web Content Accessibility Guidelines 2.0, B. Caldwell, M. Cooper, L. Guarino Reid, G. Vanderheiden et al, W3C Recommendation 11 December 2008 (see <a
|
|
href="http://www.w3.org/TR/WCAG20/">http://www.w3.org/TR/WCAG20/</a>)</dd>
|
|
<dt class="label"><a name="WEBAPPS" id="WEBAPPS">WEBAPPS</a></dt>
|
|
<dd>W3C WebApps Working Group (see <a
|
|
href="http://www.w3.org/2008/webapps/">http://www.w3.org/2008/webapps/</a>)</dd>
|
|
<dt class="label"><a name="WIDGETS" id="WIDGETS">WIDGETS</a></dt>
|
|
<dd>Widget Packaging and Configuration, Marcos Cáceres, W3C Working Draft, 5 October 2010 (see <a href="http://www.w3.org/TR/widgets/">http://www.w3.org/TR/widgets/</a>)</dd>
|
|
<dt class="label"><a name="WTAI" id="WTAI">WTAI</a></dt>
|
|
<dd>WAP Forum wap-268-wtai-20010908-a Wireless Telephony Application
|
|
Interface Specification (See <a
|
|
href="http://www.openmobilealliance.org/tech/affiliates/LicenseAgreement.asp?DocName=/wap/wap-268-wtai-20010908-a.pdf">http://www.openmobilealliance.org/tech/affiliates/LicenseAgreement.asp?DocName=/wap/wap-268-wtai-20010908-a.pdf</a>)</dd>
|
|
|
|
<dt class="label"><a name="XHTML-Basic" id="XHTML-Basic">XHTML-Basic</a></dt>
|
|
<dd>XHTML Basic 1.1 - Second Edition, Shane McCarron, Masayasu Ishikawa, Editors, W3C Recommendation, 23 November 2010 (See <a
|
|
href="http://www.w3.org/TR/2010/REC-xhtml-basic-20101123/">http://www.w3.org/TR/2010/REC-xhtml-basic-20101123/</a>)</dd>
|
|
</dl>
|
|
</div>
|
|
|
|
<h2><a id="acknowledgements" name="acknowledgements">Appendix 3:
|
|
Acknowledgments</a></h2>
|
|
|
|
<p>The editors would like to thank members of the BPWG for contributions of
|
|
various kinds. The editors would also like to thank contributors to the public
|
|
list, and contributors of Last Call comments whose comments have been taken
|
|
into account in the creation of this document.</p>
|
|
|
|
<p>The editors acknowledge significant written contributions from:</p>
|
|
|
|
<p>* Daniel Appelquist, Vodafone</p>
|
|
|
|
<p>* Jo Rabin, mTLD Mobile Top Level Domain (dotMobi)</p>
|
|
|
|
<p>* Phil Archer, W3C</p>
|
|
|
|
<p>* Jeff Sonstein, Rochester Institute of Technology</p>
|
|
|
|
<p>* François Daoust, W3C</p>
|
|
|
|
<p>* Scott Hughes, Vodafone</p>
|
|
</body>
|
|
</html>
|