Progressive enhancement is a strategy in web design that puts emphasis on web content first. This strategy involves separating the presentation semantics from the content, with presentation being implemented in one or more optional layers, activated based on aspects of the browser or Internet connection of the user. The proposed benefits of this strategy are that it allows everyone to access the basic content and functionality of a web page, whilst people with additional browser features or faster Internet access receive the enhanced version instead.
"Progressive enhancement" was coined by Steven Champeon & Nick Finck at the SXSW Interactive conference on March 11, 2003 in Austin, and through a series of articles for Webmonkey which were published between March and June 2003.
Specific Cascading Style Sheets (CSS) techniques pertaining to flexibility of the page layout accommodating different screen resolutions is the concept associated with responsive web design approach. .net Magazine chose Progressive Enhancement as #1 on its list of Top Web Design Trends for 2012 (responsive design was #2). Google has encouraged the adoption of progressive enhancement to help "our systems (and a wider range of browsers) see usable content and basic functionality when certain web design features are not yet supported".
The strategy is an evolution of a previous web design strategy known as graceful degradation, wherein Web pages were designed for the latest browsers first, but then made to work well in older versions of browser software. Graceful degradation aims to allow a page to "degrade" – to remain presentable and accessible even if certain technologies expected by the design are absent.
This section may be too technical for most readers to understand.(November 2015)
The progressive enhancement approach is derived from Champeon's early experience (c. 1993-4) with Standard Generalized Markup Language (SGML), before working with HTML or any Web presentation languages, as well as from later experiences working with CSS to work around browser bugs. In those early SGML contexts, semantic markup was of key importance, whereas presentation was nearly always considered separately, rather than being embedded in the markup itself. This concept is variously referred to in markup circles as the rule of separation of presentation and content, separation of content and style, or of separation of semantics and presentation. As the Web evolved in the mid-nineties, but before CSS was introduced and widely supported, this cardinal rule of SGML was repeatedly violated by HTML's extenders. As a result, web designers were forced to adopt new, disruptive technologies and tags in order to remain relevant. With a nod to graceful degradation, in recognition that not everyone had the latest browser, many began to simply adopt design practices and technologies only supported in the most recent and perhaps the single previous major browser releases. For several years, much of the Web simply did not work in anything but the most recent, most popular browsers. This remained true until the rise and widespread adoption of and support for CSS, as well as many populist, grassroots educational efforts (from Eric Costello, Owen Briggs, Dave Shea, and others) showing Web designers how to use CSS for layout purposes.
First proposed as a somewhat less unwieldy catchall phrase to describe the delicate art of "separating document structure and contents from semantics, presentation, and behavior", and based on the then-common use of CSS hacks to work around rendering bugs in specific browsers, the progressive enhancement strategy has taken on a life of its own as new designers have embraced the idea and extended and revised the approach.[how?]
The progressive enhancement strategy consists of the following core principles:
- Basic content should be accessible to all web browsers.
- Basic functionality should be accessible to all web browsers.
- Sparse, semantic markup contains all content.
- Enhanced layout is provided by externally linked CSS.
- End-user web browser preferences are respected.
Support and adoption
- In August 2003 Jim Wilkinson created a progressive enhancement wiki page to collect some tricks and tips and to explain the overall strategy.
- Designers such as Jeremy Keith have shown how the approach can be used harmoniously with still other approaches to modern web design (such as Ajax) to provide flexible, but powerful, user experiences.
- Others, including Dave Shea, have helped to spread the adoption of the term to refer to CSS-based design strategies.
- Organizations such as the Web Standards Project (WaSP), which was behind the creation of Acid2 and Acid3 tests, have embraced progressive enhancement as a basis for their educational efforts.
- In 2006 Nate Koechley at Yahoo! made extensive reference to progressive enhancement in his own approach to Web design and browser support, Graded Browser Support (GBS).
- Steve Chipman at AOL has referred to progressive enhancement (by DOM scripting) as a basis for his Web design strategy.
- David Artz, leader of the AOL Optimization team, developed a suite of Accessible Rendering Technologies, and invented a technique for disassembly of the "enhancement" on the fly, saving the user's preference.
- Chris Heilmann discussed the importance of targeted delivery of CSS so that each browser only gets the content (and enhancements) it can handle.
- Scott Jehl of Filament Group proposed a "Test-Driven Progressive Enhancement", recommending to test the device capabilities (rather than inferring them from the detected user agent) before providing enhancements.
- Wt is an open-source server-side web application framework which transparently implements progressive enhancement during its bootstrap, progressing from plain HTML to full Ajax.
Accessibility, compatibility, and outreach
Web pages created according to the principles of progressive enhancement are by their nature more accessible, compatible, and outreaching, because the strategy demands that basic content always be available, not obstructed by commonly unsupported or scripting that may be easily disabled, unsupported (e.g. by text-based web browsers), or blocked on computers in sensitive environments. Additionally, the sparse markup principle makes it easier for tools that read content aloud to find that content. It is unclear as to how well progressive enhancement sites work with older tools designed to deal with table layouts, "tag soup", and the like.
Speed, efficiency, and user control
The client (computing) is able to select which parts of a page to download beyond basic HTML (e.g. styling, images, etc.), and can opt only to download parts necessary for desired usage to speed up loading and reduce bandwidth and power consumption. For example, a client may choose to only download basic HTML, without loading style sheets, scripts, and media (e.g images), due to low internet speeds caused by geographical location, poor cellular signal, or throttled speed due to exhausted high-speed data plan. This also reduces bandwidth consumption on the server side.
Search engine optimization (SEO)
Criticism and responses
- Content adaptation – transforming content to adapt to device capabilities
- Flash of unstyled content
- Progressive web application
- Semantic HTML
- Universal design
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Progressive Enhancement […] means [to] build your website starting with the lowest common denominator browsers in mind.
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- Briggs, Owen; Champeon, Steven; Costello, Eric; Patternson, Matthew (2004) Cascading Style Sheets: Separating Content From Presentation (2nd ed.). San Francisco: Apress. ISBN 1-59059-231-X
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- Keith, Jeremy (2007) Bulletproof Ajax. Berkeley: New Riders. ISBN 0-321-47266-7
- Parker, Todd; Toland, Patty; Jehl, Scott; Costello Wachs, Maggie (The Filament Group) (2010) Designing with Progressive Enhancement Peachpit/New Riders. ISBN 978-0-321-65888-3