Progressive enhancement

Progressive enhancement is a strategy for web design that emphasizes accessibility, semantic HTML markup, and external stylesheet and scripting technologies. Progressive enhancement uses web technologies in a layered fashion that allows everyone to access the basic content and functionality of a web page, using any browser or Internet connection, while also providing an enhanced version of the page to those with more advanced browser software or greater bandwidth.

History

"Progressive Enhancement" was coined by Steven Champeon in a series of articles and presentations for Webmonkey and the SXSW Interactive conference between March and June 2003.^[1][2]

Specific CSS techniques pertaining to flexibility of the page layout accommodating different screen resolutions is recently being discussed under the name of "Responsive Web Design". .net Magazine chose Progressive Enhancement as #1 on its list of Top Web Design Trends for 2012 (Responsive design was #2).^[3]

Introduction and background

The strategy is an evolution of a previous web design strategy known as "graceful degradation", wherein designers would create Web pages for the latest browsers that would also work well in older versions of browser software. Graceful degradation was supposed to allow the page to "degrade", or remain presentable even if certain technologies assumed by the design were not present, without being jarring to the user of such older software. In practice, graceful degradation has been supplanted by an attitude that the end user should "just upgrade".^{[citation needed]} This attitude is due to time and budget constraints, limited access to testing alternate browser software, as well as the widespread belief that "browsers are free". Unfortunately, upgrading is often not possible due to IT department policies, older hardware, and other reasons. The "just upgrade" attitude also ignores deliberate user choices and the existence of a variety of browser platforms; many of which run on handhelds or in other contexts where available bandwidth is restricted, or where support for sound or color and limited screen size, for instance, are far different from the typical graphical desktop browser. There is also a large group of Internet users unaware or uncaring about the features of the browser.

In Progressive Enhancement (PE) the strategy is deliberately reversed: a basic markup document is created, geared towards the lowest common denominator of browser software functionality, and then the designer adds in functionality or enhancements to the presentation and behavior of the page, using modern technologies such as Cascading Style Sheets or JavaScript (or other advanced technologies, such as Flash or Java applets or SVG, etc.). All such enhancements are externally linked, preventing data unusable by certain browsers from being unnecessarily downloaded.

The PE approach is derived from Champeon's early experience (c. 1993-4) with 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.

PE is based on a recognition that the core assumption behind "graceful degradation" — that browsers always got faster and more powerful — was proving itself false with the rise of handheld and PDA devices with low-functionality browsers and serious bandwidth constraints. In addition, the rapid evolution of HTML and related technologies in the early days of the Web has slowed, and very old browsers have become obsolete, freeing designers to use powerful technologies such as CSS to manage all presentation tasks and JavaScript to enhance complex client-side behavior.

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 PE strategy has taken on a life of its own as new designers have embraced the idea and extended and revised the approach.

Core principles

Progressive Enhancement 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
• enhanced behavior is provided by unobtrusive, externally linked JavaScript
• end-user web browser preferences are respected

Support and adoption

• Jim Wilkinson created a page for Progressive Enhancement Wiki to collect some tricks and tips and to explain the overall strategy.^[4]
• 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.^[5]
• 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, which was behind the creation of Acid2 and Acid3 tests, have embraced PE as a basis for their educational efforts.
• In 2006 Nate Koechley at Yahoo! made extensive reference to PE in his own approach to Web design and browser support, Graded Browser Support (GBS).^[6]
• Steve Chipman at AOL has referred to PE (by DOM scripting) as a basis for his Web design strategy.^[7]
• 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.^[8]
• Scott Jehl of Filament Group introduced "Test-Driven Progressive Enhancement" on A List Apart in 2008. The article proposes testing browser capabilities (rather than detecting the user-agent and inferring capabilities) before applying enhancements, to ensure a usable experience to the largest audience possible.
• 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.

Benefits for accessibility

Web pages created according to the principles of PE are by their nature more accessible, because the strategy demands that basic content always be available, not obstructed by commonly unsupported or easily disabled scripting. 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 PE sites work with older tools designed to deal with table layouts, "tag soup," and the like.

Benefits for search engine optimization (SEO)

Improved results with respect to search engine optimization is another side effect of a PE-based Web design strategy. Because the basic content is always accessible to search engine spiders, pages built with PE methods avoid problems that may hinder search engine indexing.^[9]

Criticism and responses

Some skeptics, such as Garret Dimon, have expressed their concern that PE is not workable in situations that rely heavily on JavaScript to achieve certain user interface presentations or behaviors,^[10] to which unobtrusive JavaScript is one response. Others have countered with the point that informational pages should be coded using PE in order to be indexed by spiders,^[11] and that even Flash-heavy pages should be coded using PE.^[12] In a related area, many have expressed their doubts concerning the principle of the separation of content and presentation in absolute terms, pushing instead for a realistic recognition that the two are inextricably linked.^[13][14]

See also

• Content adaptation transform content to adapt to device capabilities.
• jQuery Mobile
• Unobtrusive JavaScript
• Ajax
• Graceful degradation
• Liquid layout
• Semantic HTML

Notes

References

Further reading

Articles

Books

External links

• Color Vision - by Cal Henderson
• The W3C Markup Validation Service