Web style sheets are a form of separation of presentation and content Separation of presentation and content is a common idiom, a design philosophy, and a methodology applied in the context of various publishing technology disciplines, including information retrieval, , web design, web development, word processing, desktop publishing, and model-driven development. It is a specific instance of the more general for web design Web design is the skill of creating presentations of content that is delivered to an end-user through the World Wide Web, using a Web browser or other Web-enabled software . The intent of web design is to create a website—a collection of electronic documents and applications that reside on a Web server/servers. The website may include text, in which the markup A markup language is a system for annotating a text in a way which is syntactically distinguishable from that text. Examples include revision instructions by editors, traditionally written with a blue pencil on authors' manuscripts, typesetting instructions such those found in troff and LaTeX, and structural markers such as XML tags. Markup is (i.e., HTML HTML, which stands for HyperText Markup Language, is the predominant markup language for web pages. It is written in the form of HTML elements consisting of "tags" surrounded by angle brackets within the web page content or XHTML XHTML is a family of XML markup languages that mirror or extend versions of the widely used Hypertext Markup Language (HTML), the language in which web pages are written) of a webpage A web page or webpage is a document or resource of information that is suitable for the World Wide Web and can be accessed through a web browser and displayed on a monitor or mobile device contains the page's semantic content and structure, but does not define its visual layout (style). Instead, the style is defined in an external stylesheet file using a style sheet language A style sheet language or style language, is a computer language used to describe the presentation of structured documents. A structured document which doesn't break the schema it is designed to conform to is "well-formed". A program processing the document must model the schema, and can present it in different formats, fonts, and order, such as CSS Cascading Style Sheets is a style sheet language used to describe the presentation semantics (that is, the look and formatting) of a document written in a markup language. Its most common application is to style web pages written in HTML and XHTML, but the language can also be applied to any kind of XML document, including SVG and XUL or XSL In computing, the term Extensible Stylesheet Language is used to refer to a family of languages used for transforming and rendering XML documents. This design approach is identified as a "separation" because it largely supersedes the antecedent methodology in which a page's markup defined both style and structure.
The philosophy underlying this methodology is a specific case of separation of concerns In computer science, separation of concerns is the process of separating a computer program into distinct features that overlap in functionality as little as possible. A concern is any piece of interest or focus in a program. Typically, concerns are synonymous with features or behaviors. Progress towards SoC is traditionally achieved through.
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Benefits
Separation of style and content has many benefits, but has only become practical in recent years due to improvements in popular web browsers A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users to easily navigate their browsers to' CSS implementations.
Speed
Overall, users experience of a site utilising style sheets will generally be quicker than sites that don’t use the technology. ‘Overall’ as the first page will probably load more slowly – because the style sheet AND the content will need to be transferred. Subsequent pages will load faster because no style information will need to be downloaded – the CSS file will already be in the browser's cache.
Maintainability
Holding all the presentation styles in one file significantly reduces maintenance time and reduces the chance of human errors, thereby improving presentation consistency. For example, the font color associated with a type of text element may be specified — and therefore easily modified — throughout an entire website simply by changing one short string of characters in a single file. The alternate approach, using styles embedded in each individual page, would require a cumbersome, time consuming, and error-prone edit of every file.
Accessibility
Sites that use CSS with either XHTML or HTML are easier to tweak so that they appear extremely similar in different browsers (Internet Explorer Windows Internet Explorer , is a series of graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems starting in 1995. It has been the most widely used web browser since 1999, attaining a peak of about 95% usage share during 2002 and 2003 with IE5 and IE6, Mozilla Firefox Mozilla Firefox is a free and open source web browser descended from the Mozilla Application Suite and managed by Mozilla Corporation. A Net Applications statistic put Firefox at 24.59% of the recorded usage share of web browsers as of April 2010[update], making it the second most popular browser in terms of current use worldwide after Microsoft's, Opera Opera is a web browser and Internet suite developed by Opera Software. The browser handles common Internet-related tasks such as displaying web sites, sending and receiving e-mail messages, managing contacts, chatting on IRC, downloading files via BitTorrent, and reading Web feeds. Opera is offered free of charge for personal computers and mobile, Safari Safari is a graphical web browser developed by Apple and included as part of the Mac OS X operating system. First released as a public beta on January 7, 2003 on the company's Mac OS X operating system, it became Apple's default browser beginning with Mac OS X v10.3 "Panther." Safari is also the native browser for the iPhone OS. A, etc.).
Sites using CSS "degrade gracefully Fault-tolerance or graceful degradation is the property that enables a system to continue operating properly in the event of the failure of (or one or more faults within) some of its components. If its operating quality decreases at all, the decrease is proportional to the severity of the failure, as compared to a naïvely-designed system in which" in browsers unable to display graphical content, such as Lynx, or those so very old that they cannot use CSS. Browsers ignore CSS that they do not understand, such as CSS 3 statements. This enables a wide variety of user agents A user agent is a client application implementing a network protocol used in communications within a client–server distributed computing system. The term most notably refers to applications that access the World Wide Web, but other systems, such as the Session Initiation Protocol , use the term user agent to refer to both end points of a to be able to access the content of a site even if they cannot render the stylesheet or are not designed with graphical capability in mind. For example, a browser using a refreshable braille display for output could disregard layout information entirely, and the user would still have access to all page content.
Customization
If a page's layout information is all stored externally, a user can decide to disable the layout information entirely, leaving the site's bare content still in a readable form. Site authors may also offer multiple stylesheets, which can be used to completely change the appearance of the site without altering any of its content.
Most modern web browsers also allow the user to define their own stylesheet, which can include rules that override the author's layout rules. This allows users, for example, to bold every hyperlink on every page they visit.
Consistency
Because the semantic file contains only the meanings an author intends to convey, the styling of the various elements of the document's content is very consistent. For example, headings, emphasized text, lists and mathematical expressions all receive consistently applied style properties from the external stylesheet. Authors need not concern themselves with the style properties at the time of composition. These presentational details can be deferred until the moment of presentation.
Portability
The deferment of presentational details until the time of presentation means that a document can be easily re-purposed for an entirely different presentation medium with merely the application of a new stylesheet already prepared for the new medium and consistent with elemental or structural vocabulary of the semantic document. A carefully authored document for a web page can easily be printed to a hard-bound volume complete with headers and footers, page numbers and a generated table of contents simply by applying a new stylesheet.
Practical disadvantages today
Currently specifications (for example, XHTML, XSL, CSS) and software tools implementing these specification are only reaching the early stages of maturity. So there are some practical issues facing authors who seek to embrace this method of separating content and style.
Complex layouts
One of the practical problems is the lack of proper support for style languages in major browsers. Typical web page layouts call for some tabular presentation of the major parts of the page such as menu navigation columns and header bars, navigation tabs, and so on. However, deficient support for CSS and XSL in major browsers forces authors to code these tables within their content rather than applying a tabular style to the content from the accompanying stylesheet.
Narrow adoption without the parsing and generation tools
While the style specifications are quite mature and still maturing, the software tools have been slow to adapt. Most of the major web development tools still embrace a mixed presentation-content model. So authors and designers looking for GUI based tools for their work find it difficult to follow the semantic web method. In addition to GUI tools, shared repositories for generalized stylesheets would probably aid adoption of these methods.
See also
External resources
- Simply JavaScript: The Three Layers of the Web
- CSS Zen Garden: A site which challenges designers to create new page layouts without touching the XHTML source. Includes dozens of layouts. CSS source can be viewed for every layout.
- Revealed – Our HTML and CSS Codes – cameraontheroad.com: Gives practical examples of CSS advantages from a site which has moved from embedded presentation styles to style sheets. Includes links to CSS resources.
- Brugbart: A site holding Tutorials and References to CSS based, and standard compliant layouts.
- SLIRK: A new css/javascript website layout approach.
- Free css menus: A website using advanced techniques in css. Menus, buttons and rollover animations. Unlike other css websites that showcase css design, this one allows users to upload just about any type of css creativity. There is also an online css menu creator, allowing users to create vertical or horizontal css menus without programming any code, all of which are w3c compliant.
Categories: Web development
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hu, 05 Aug 2010 21:36:37 GM
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Asked by belikeyeshua - Thu Mar 26 08:29:48 2009 - - 6 Answers - 0 Comments
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Answered by Gus - Thu Mar 26 08:54:56 2009
