“Progressive enhancement”的意思、由来-开放百科全书

Progressive enhancement is a strategy for web design that emphasizes core webpage content first. This strategy then progressively adds more nuanced and technically rigorous layers of presentation and features on top of the content as the end-user's browser/internet connection allow. The proposed benefits of this strategy are that it 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 & Nick Finck at the SXSW Interactive conference on March 11, 2003 in Austin,^[1] and through a series of articles for Webmonkey which were published between March and June 2003.^[2]

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).^[3] 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".^[4]

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|date=July 2017}}

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, Scalable Vector Graphics (SVG), or JavaScript. 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 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,^[5] 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

Support and adoption

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 (SEO) 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.^[15]

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,^[16] 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,^[17] and that even Flash-heavy pages should be coded using PE.^[18] 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.^[19]^[20]

See also

Notes

1. ^Champeon, Steven & Finck, Nick (2003) Inclusive Web Design for the Future, SxSWi presentation
2. ^Champeon, Steven (2003), Progressive Enhancement and the Future of Web Design, Webmonkey
3. ^{{cite web|title=15 top web design and development trends for 2012|date=January 9, 2012|url=http://www.creativebloq.com/features/15-top-web-design-and-development-trends-for-2012/}}
4. ^Pierre Far (2014), Updating our technical Webmaster Guidelines, Webmaster Central Blog
5. ^{{cite web |title=Zen and the Art of Web Improvement |url=http://www.mezzoblue.com/archives/pres/we04/designing/index.php |accessdate=14 April 2006}}
6. ^Wilkinson, Jim (2003), Progressive Enhancement - CSS Discuss
7. ^Jeremy Keith's Adactio blog (2005), Progressive Enhancement with Ajax
8. ^Aaron Gustafson (2008), Understanding Progressive Enhancement, A List Apart
9. ^Aaron Gustafson (2008), Progressive Enhancement with CSS, A List Apart
10. ^Aaron Gustafson (2008), Progressive Enhancement with JavaScript, A List Apart
11. ^Nate Koechley, Graded Browser Support {{webarchive|url=https://web.archive.org/web/20060414110338/http://developer.yahoo.com/yui/articles/gbs/gbs.html |date=2006-04-14 }}
12. ^Steven G. Chipman (2005), New Skool DOM Scripting
13. ^Chris Heilmann, Double Vision – Give the Browsers CSS They Can Digest (2005)
14. ^{{cite web|last1=Jehl|first1=Scott|title=Test Driven Progressive Enhancement|url=http://alistapart.com/article/testdriven|website=A List Apart|accessdate=27 October 2009}}
15. ^Stephan Spencer, PE is good for SEO | Searchlight - CNET News
16. ^Dimon, Garret, The Reality of Progressive Enhancement {{webarchive|url=https://web.archive.org/web/20070317045908/http://v1.garrettdimon.com/archives/the-reality-of-progressive-enhancement |date=2007-03-17 }}
17. ^IA Summit 2006 » Blog Archive » Web 2.0 and SEO? {{webarchive|url=https://web.archive.org/web/20060417210246/http://iasummit.org/2006/blog/?p=86 |date=2006-04-17 }}
18. ^deconcept » Using alternate content as content in Flash
19. ^Stopdesign | Are They Really Separated? (2003)
20. ^A List Apart: Articles: Separation Anxiety: The Myth of the Separation of Style from Content (2000)