WEB DESIGNING LANGAUGE

Cascading Style Sheets (CSS)--
CSS is a style sheet language used for describing the presentation semantics (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 plain XML, SVG and XUL.

CSS is designed primarily to enable the separation of document content (written in HTML or a similar markup language) from document presentation, including elements such as the layout, colors, and fonts. This separation can improve content accessibility, provide more flexibility and control in the specification of presentation characteristics, enable multiple pages to share formatting, and reduce complexity and repetition in the structural content (such as by allowing for tableless web design). CSS can also allow the same markup page to be presented in different styles for different rendering methods, such as on-screen, in print, by voice (when read out by a speech-based browser or screen reader) and on Braille-based, tactile devices. It can also be used to allow the web page to display differently depending on the screen size or device on which it is being viewed. While the author of a document typically links that document to a CSS style sheet, readers can use a different style sheet, perhaps one on their own computer, to override the one the author has specified.

CSS specifies a priority scheme to determine which style rules apply if more than one rule matches against a particular element. In this so-called cascade, priorities or weights are calculated and assigned to rules, so that the results are predictable.

The CSS specifications are maintained by the World Wide Web Consortium (W3C). Internet media type (MIME type) texcss is registered for use with CSS by RFC 2318 (March 1998), and they also operate a free CSS validation service.

Syntax

CSS has a simple syntax and uses a number of English keywords to specify the names of various style properties.

A style sheet consists of a list of rules. Each rule or rule-set consists of one or more selectors, and a declaration block. A declaration-block consists of a list of declarations in braces. Each declaration itself consists of a property, a colon (:), and a value. If there are multiple declarations in a block, a semi-colon (;) must be inserted to separate each declaration.

In CSS, selectors are used to declare which part of the markup a style applies to, a kind of match expression. Selectors may apply to all elements of a specific type, to elements specified by attribute, or to elements depending on how they are placed relative to, or nested within, others in the document tree.

Pseudo-classes are used in CSS selectors to permit formatting based on information that is outside the document tree. An often-used example of a pseudo-class is :hover, which identifies content only when the user 'points to' the visible element, usually by holding the mouse cursor over it. It is appended to a selector as in a:hover or #elementid:hover. A pseudo-class classifies document elements, such as :link or :visited, whereas a pseudo-element makes a selection that may consist of partial elements, such as:first-line or :first-letter.

Selectors may be combined in many ways, especially in CSS 2.1, to achieve great specificity and flexibility.

Here is an example using the above rules:

selector [, selector2, ...] [:pseudo-class] {
 property: value;
 [property2: value2;
 ...]
}
/* comment */

USE Prior to CSS, nearly all of the presentational attributes of HTML documents were contained within the HTML markup; all font colors, background styles, element alignments, borders and sizes had to be explicitly described, often repeatedly, within the HTML. CSS allows authors to move much of that information to another file, the style sheet, resulting in considerably simpler HTML.

Headings (h1 elements), sub-headings (h2), sub-sub-headings (h3), etc., are defined structurally using HTML. In print and on the screen, choice of font, size, color and emphasisfor these elements is presentational.

Prior to CSS, document authors who wanted to assign such typographic characteristics to, say, all h2 headings had to repeat HTML presentational markup for each occurrence of that heading type. This made documents more complex, larger, and more difficult to maintain. CSS allows the separation of presentation from structure. CSS can define color, font, text alignment, size, borders, spacing, layout and many other typographic characteristics, and can do so independently for on-screen and printed views. CSS also defines non-visual styles such as the speed and emphasis with which text is read out by aural text readers. The W3C has now deprecated the use of all presentational HTML markup.^]

CSS files can be associated with HTML documents using the following syntax:

<link rel="stylesheet" href="http://example.com/css/style.css" type="text/css" />                                                                                                                                              

CSS information can be provided from various sources. CSS style information can be in a separate document or it can be embedded into an HTML document. Multiple style sheets can be imported. Different styles can be applied depending on the output device being used; for example, the screen version can be quite different from the printed version, so that authors can tailor the presentation appropriately for each medium.

Priority scheme for CSS sources (from highest to lowest priority):

• Author styles (provided by the web page author), in the form of:
  • Inline styles, inside the HTML document, style information on a single element, specified using the style attribute
  • Embedded style, blocks of CSS information inside the HTML itself
  • External style sheets, i.e., a separate CSS file referenced from the document
• User style:
  • A local CSS file the user specifies with a browser option, which acts as an override applied to all documents
• User agent style
  • Default styles applied by the user agent, i.e., the browser's default settings for each element's presentation

The style sheet with the highest priority controls the content display. Declarations not set in the highest priority source are passed on to a source of lower priority, such as the user agent style. This process is called cascading.

One of the goals of CSS is also to allow users greater control over presentation. Someone who finds red italic headings difficult to read may apply a different style sheet. Depending on the browser and the web site, a user may choose from various style sheets provided by the designers, or may remove all added styles and view the site using the browser's default styling, or may override just the red italic heading style without altering other attributes.

Style sheets have existed in one form or another since the beginnings of SGML in the 1980s. Cascading Style Sheets were developed as a means for creating a consistent approach to providing style information for web documents.

As HTML grew, it came to encompass a wider variety of stylistic capabilities to meet the demands of web developers. This evolution gave the designer more control over site appearance, at the cost of more complex HTML. Variations in web browser implementations, such as ViolaWWWand WorldWideWe made consistent site appearance difficult, and users had less control over how web content was displayed. Robert Cailliauwanted to separate the structure from the presentation. The ideal way would be to give the user different options and transferring three different kinds of style sheets: one for printing, one for the presentation on the screen and one for the editor feature.

To improve web presentation capabilities, nine different style sheet languages were proposed to the World Wide Web Consortium's (W3C) www-style mailing list. Of the nine proposals, two were chosen as the foundation for what became CSS: Cascading HTML Style Sheets (CHSS) and Stream-based Style Sheet Proposal (SSP). CHSS, a language that has some resemblance to today's CSS, was proposed by Håkon Wium Lie in October 1994. Bert Bos was working on a browser called Argo, which used its own style sheet language called SSP. Lie and Yves Lafon joinedDave Raggett to expand the Arena browser for supporting CSS as a testbed application for the W3C. Lie and Bos worked together to develop the CSS standard (the 'H' was removed from the name because these style sheets could also be applied to other markup languages besides HTML).

Unlike existing style languages like DSSSL and FOSI, CSS allowed a document's style to be influenced by multiple style sheets. One style sheet could inherit or "cascade" from another, permitting a mixture of stylistic preferences controlled equally by the site designer and user.

Lie's proposal was presented at the "Mosaic and the Web" conference (later called WWW2) in Chicago, Illinois in 1994, and again with Bert Bos in 1995. Around this time the W3C was already being established, and took an interest in the development of CSS. It organized a workshop toward that end chaired by Steven Pemberton. This resulted in W3C adding work on CSS to the deliverables of the HTML editorial review board (ERB). Lie and Bos were the primary technical staff on this aspect of the project, with additional members, including Thomas Reardon of Microsoft, participating as well. In August 1996 Netscape Communication Corporation presented an alternative style sheet language calledJavaScript Style Sheets (JSSS). The spec was never finished and is deprecated. By the end of 1996, CSS was ready to become official, and the CSS level 1 Recommendation was published in December.

Development of HTML, CSS, and the DOM had all been taking place in one group, the HTML Editorial Review Board (ERB). Early in 1997, the ERB was split into three working groups: HTML Working group, chaired by Dan Connolly of W3C; DOM Working group, chaired by Lauren Wood of SoftQuad; and CSS Working group, chaired by Chris Lilley of W3C.

The CSS Working Group began tackling issues that had not been addressed with CSS level 1, resulting in the creation of CSS level 2 on November 4, 1997. It was published as a W3C Recommendation on May 12, 1998. CSS level 3, which was started in 1998, is still under development as of 2009.

In 2005 the CSS Working Groups decided to enforce the requirements for standards more strictly. This meant that already published standards like CSS 2.1, CSS 3 Selectors and CSS 3 Text were pulled back from Candidate Recommendation to Working Draft level.
Difficulty with adoption

The CSS 1 specification was completed in 1996. Microsoft's Internet Explorer 3was released in that year, featuring some limited support for CSS. But it was more than three years before any web browser achieved near-full implementation of the specification. Internet Explorer 5.0 for the Macintosh, shipped in March 2000, was the first browser to have full (better than 99 percent) CSS 1 support,surpassing Opera, which had been the leader since its introduction of CSS support 15 months earlier. Other browsers followed soon afterwards, and many of them additionally implemented parts of CSS 2. As of August 2010, no (finished) browser has fully implemented CSS 2, with implementation levels varying (see Comparison of layout engines (CSS)).

Even though early browsers such as Internet Explorer 3 and 4, and Netscape 4.x had support for CSS, it was typically incomplete and had serious bugs. This was a serious obstacle for the adoption of CSS.

When later 'version 5' browsers began to offer a fairly full implementation of CSS, they were still incorrect in certain areas and were fraught with inconsistencies, bugs and otherquirks. The proliferation of such CSS-related inconsistencies and even the variation in feature support has made it difficult for designers to achieve a consistent appearance across browsers and platforms. Some authors resorted to workarounds such as CSS hacks and CSS filters.

Problems with browsers' patchy adoption of CSS, along with errata in the original specification, led the W3C to revise the CSS 2 standard into CSS 2.1, which moved nearer to a working snapshot of current CSS support in HTML browsers. Some CSS 2 properties that no browser successfully implemented were dropped, and in a few cases, defined behaviors were changed to bring the standard into line with the predominant existing implementations. CSS 2.1 became a Candidate Recommendation on February 25, 2004, but CSS 2.1 was pulled back to Working Draft status on June 13, 2005, and only returned to Candidate Recommendation status on July 19, 2007.

In the past, some web servers were configured to serve all documents with the filename extension .css as mime type application/x-pointplus rather thantext/css. At the time, the Net-Scene company was selling PointPlus Maker to convert PowerPoint files into Compact Slide Show files (using a .css extension).

CSS has various levels and profiles. Each level of CSS builds upon the last, typically adding new features and typically denoted as CSS 1, CSS 2, CSS 3, and CSS 4. Profiles are typically a subset of one or more levels of CSS built for a particular device or user interface. Currently there are profiles for mobile devices, printers, and television sets. Profiles should not be confused with media types, which were added in CSS 2.

CSS 1

The first CSS specification to become an official W3C Recommendation is CSS level 1, published in December 1996. Among its capabilities are support for

• Font properties such as typeface and emphasis
• Color of text, backgrounds, and other elements
• Text attributes such as spacing between words, letters, and lines of text
• Alignment of text, images, tables and other elements
• Margin, border, padding, and positioning for most elements
• Unique identification and generic classification of groups of attributes

The W3C no longer maintains the CSS 1 Recommendation.

CSS 2

CSS level 2 specification was developed by the W3C and published as a recommendation in May 1998. A superset of CSS 1, CSS 2 includes a number of new capabilities like absolute, relative, and fixed positioning of elements and z-index, the concept of media types, support for aural style sheets and bidirectional text, and new font properties such as shadows.

The W3C no longer maintains the CSS 2 recommendation.

CSS level 2 revision 1, often referred to as "CSS 2.1", fixes errors in CSS 2, removes poorly supported or not fully interoperable features and adds already-implemented browser extensions to the specification. In order to comply with the W3C Process for standardizing technical specifications, CSS 2.1 went back and forth between Working Draft status and Candidate Recommendation status for many years. CSS 2.1 first became a Candidate Recommendation on February 25, 2004, but it was reverted to a Working Draft on June 13, 2005 for further review. It returned to Candidate Recommendation on 19 July 2007 and then updated twice in 2009. However, since changes and clarifications were made, it again went back to Last Call Working Draft on 7 December 2010.

CSS 2.1 went to Proposed Recommendation on 12 April 2011. After being reviewed by the W3C Advisory Committee, it was finally published as a W3C Recommendation on 7 June 2011.

"CSS3" redirects here. For airport code CSS3, see Montréal/Les Cèdres Airport.

Unlike CSS 2, which is a large single specification defining various features, CSS 3 is divided into several separate documents called "modules". Each module adds new capabilities or extends features defined in CSS 2, over preserving backward compatibility. Work on CSS level 3 started around the time of publication of the original CSS 2 recommendation. The earliest CSS 3 drafts were published in June 1999.

Due to the modularization, different modules have different stability and statuses. As of June 2012, there are over fifty CSS modules published from the CSS Working Group.,and four of these have been published as formal recommendations:

• 2012-06-19 : Media Queries
• 2011-09-29 : Namespaces
• 2011-09-29 : Selectors Level 3
• 2011-06-07 : Color

Some modules (including Backgrounds and Borders and Multi-column Layout among others) have Candidate Recommendation (CR) status and are considered moderately stable. At CR stage, implementations are advised to drop vendor prefixes.

CSS 3 also supports adding round edges to elements via the border-radius property. Increasingly more websites are utilizing this technique for aesthetic purposes.

W3C started drafting CSS 4 on September 29, 2009. However, it is currently not supported by any major web browser.

One of the new proposed selectors is :matches(). For which

:matches(div, p, nav) span{
    font-size: 18px;
}

is the same as:

div span, p span, nav span{
    font-size: 18px;
}

Although Gecko and WebKit already have similar functions:

/* Gecko */
-moz-any(div, p, nav) span{
  font-size: 18px;
}
/* Webkit */
-webkit-any(div, p, nav) span{
  font-size: 18px;
}

Another interesting and especially very usable way are reference combinators. Those allow you to select elements that are referenced by ID by another element, like a form element. The attendant label reference is the "for attribute". You can define a reference combinator by the attribute with forward slashes (/). In case of an input element you wanted to style different (from grey to blue) when you hover its label, you could use the selector label:hover /for/ input.

label:hover /for/ input {
  border-color:blue;
}

Browser support

Further information: Comparison of layout engines (Cascading Style Sheets)

Because not all browsers correctly parse CSS code, developed coding techniques known as CSS hacks can either filter specific browsers or target specific browsers (generally both are known as CSS filters). The former can be defined as CSS filtering hacks and the latter can be defined as CSS targeting hacks. Both can be used to hide or show parts of the CSS to different browsers. This is achieved either by exploiting CSS-handling quirks or bugs in the browser, or by taking advantage of lack of support for parts of the CSS specifications. Using CSS filters, some designers have gone as far as delivering different CSS to certain browsers to ensure designs render as expected. Because very early web browsers were either completely incapable of handling CSS, or rendered CSS very poorly, designers today often routinely use CSS filters that completely prevent these browsers from accessing any of the CSS. Internet Explorer support for CSS began with IE 3.0 and increased progressively with each version. By 2008, the first Beta of Internet Explorer 8offered support for CSS 2.1 in its best web standards mode.

An example of a well-known CSS browser bug is the Internet Explorer box model bug, where box widths are interpreted incorrectly in several versions of the browser, resulting in blocks that are too narrow when viewed in Internet Explorer, but correct in standards-compliant browsers. The bug can be avoided in Internet Explorer 6 by using the correct doctypein (X)HTML documents. CSS hacks and CSS filters are used to compensate for bugs such as this, just one of hundreds of CSS bugs that have been documented in various versions of Netscape, Mozilla Firefox, Opera, and Internet Explorer (including Internet Explorer 7).

Even when the availability of CSS-capable browsers made CSS a viable technology, the adoption of CSS was still held back by designers' struggles with browsers' incorrect CSS implementation and patchy CSS support. Even today, these problems continue to make the business of CSS design more complex and costly than it was intended to be, andcross-browser testing remains a necessity. Other reasons for the continuing non-adoption of CSS are: its perceived complexity, authors' lack of familiarity with CSS syntax and required techniques, poor support from authoring tools, the risks posed by inconsistency between browsers and the increased costs of testing.

Currently there is strong competition between Mozilla's Gecko layout engine used in Firefox, the WebKit layout engine used in Apple Safari and Google Chrome, the similar KHTMLengine used in KDE's Konqueror browser, and Opera's Presto layout engine—each of them is leading in different aspects of CSS.^[ As of August 2009, Internet Explorer 8, Firefox 2 and 3 have reasonably complete levels of implementation of CSS 2.1.

Some noted limitations of the current capabilities of CSS include:

Poor controls for flexible layouts 

While new additions to CSS 3 provide a stronger, more robust feature-set for layout, CSS is still at heart a styling language (for fonts, colours, borders and other decoration), not a layout language (for blocks with positions, sizes, margins, and so on). These limitations mean that creating fluid layouts generally requires hand-coding of CSS, and has held back the development of a standards-based WYSIWYG editor.

Selectors are unable to ascend

CSS offers no way to select a parent or ancestor of an element that satisfies certain criteria.A more advanced selector scheme (such as XPath) would enable more sophisticated style sheets. However, the major reasons for the CSS Working Group rejecting proposals for parent selectors are related to browser performance and incremental rendering issues.

Vertical control limitations 

While horizontal placement of elements is generally easy to control, vertical placement is frequently unintuitive, convoluted, or outright impossible. Simple tasks, such as centering an element vertically or getting a footer to be placed no higher than bottom of viewport, either require complicated and unintuitive style rules, or simple but widely unsupported rules.

Absence of expressions 

There is currently no ability to specify property values as simple expressions (such as margin-left: 10% – 3em + 4px;). This would be useful in a variety of cases, such as calculating the size of columns subject to a constraint on the sum of all columns. However, a working draft with a calc() value to address this limitation has been published by the CSS WG. Internet Explorer versions 5 to 7 support a proprietary expression() statement, with similar functionality. This proprietary expression() statement is no longer supported from Internet Explorer 8 onwards, except in compatibility modes. This decision was taken for "standards compliance, browser performance, and security reasons".

Lack of column declaration 

While possible in current CSS 3 (using the column-count module), layouts with multiple columns can be complex to implement in CSS 2.1. With CSS 2.1, the process is often done using floating elements, which are often rendered differently by different browsers, different computer screen shapes, and different screen ratios set on standard monitors.

Cannot explicitly declare new scope independently of position 

Scoping rules for properties such as z-index look for the closest parent element with a position:absolute or position:relative attribute. This odd coupling has undesired effects. For example, it is impossible to avoid declaring a new scope when one is forced to adjust an element's position, preventing one from using the desired scope of a parent element.

Pseudo-class dynamic behavior not controllable 

CSS implements pseudo-classes that allow a degree of user feedback by conditional application of alternate styles. One CSS pseudo-class, ":hover", is dynamic (equivalent of JavaScript "onmouseover") and has potential for abuse (e.g., implementing cursor-proximity popups),but CSS has no ability for a client to disable it (no "disable"-like property) or limit its effects (no "nochange"-like values for each property).

Cannot name rules 

There is no way to name a CSS rule, which would allow (for example) client-side scripts to refer to the rule even if its selector changes.

Cannot include styles from a rule into another rule 

CSS styles often must be duplicated in several rules to achieve a desired effect, causing additional maintenance and requiring more thorough testing.

Cannot target specific text without altering markup 

Besides the :first-letter pseudo-element, one cannot target specific ranges of text without needing to utilize place-holder elements.

Advantages

Separation of content from presentation

CSS facilitates publication of content in multiple presentation formats based on nominal parameters. Nominal parameters include explicit user preferences, different web browsers, the type of device being used to view the content (a desktop computer or mobile Internet device), the geographic location of the user and many other variables.

Site-wide consistency

Main articles: Separation of presentation and content and Style sheet (web development)

When CSS is used effectively, in terms of inheritance and "cascading," a global style sheet can be used to affect and style elements site-wide. If the situation arises that the styling of the elements should need to be changed or adjusted, these changes can be made by editing rules in the global style sheet. Before CSS, this sort of maintenance was more difficult, expensive and time-consuming.

Bandwidth

A stylesheet, internal or external, will specify the style once for a range of HTML elements selected by class, type or relationship to others. This is much more efficient than repeating style information inline for each occurrence of the element. An external stylesheet is usually stored in the browser cache, and can therefore be used on multiple pages without being reloaded, further reducing data transfer over a network.

Page reformatting

Main article: Progressive enhancement

With a simple change of one line, a different style sheet can be used for the same page. This has advantages for accessibility, as well as providing the ability to tailor a page or site to different target devices. Furthermore, devices not able to understand the styling still display the content.

Accessibility

Without CSS, web designers must typically lay out their pages with techniques that hinder accessibility for vision-impaired users, like HTML tables (see Tableless web design#Accessibility).

CSS frameworks

CSS frameworks are pre-prepared libraries that are meant to allow for easier, more standards-compliant styling of web pages using the Cascading Style Sheets language. Layout-grid-related CSS frameworks include Blueprint, 960 grid, and YUI CSS grids. Like programming and scripting language libraries, CSS frameworks are usually incorporated as external .css sheets referenced in the HTML <head>. They provide a number of ready-made options for designing and laying out the web page. While many of these frameworks have been published, some authors use them mostly for rapid prototyping, or for learning from, and prefer to 'handcraft' CSS that is appropriate to each published site without the design, maintenance and download overhead of having many unused features in the site's styling.

Positioning

CSS 2.1 defines three positioning schemes:

Normal flow

Inline items are laid out in the same way as the letters in words in text, one after the other across the available space until there is no more room, then starting a new line below.Block items stack vertically, like paragraphs and like the items in a bulleted list. Normal flow also includes relative positioning of block or inline items, and run-in boxes.

Floats

A floated item is taken out of the normal flow and shifted to the left or right as far as possible in the space available. Other content then flows alongside the floated item.

Absolute positioning

An absolutely positioned item has no place in, and no effect on, the normal flow of other items. It occupies its assigned position in its container independently of other items.

Position: top, bottom, left, and right

There are four possible values of the position property. If an item is positioned in any way other than static, then the further properties top, bottom, left, and right are used to specify offsets and positions.

Static

The default value places the item in the normal flow

Relative

The item is placed in the normal flow, and then shifted or offset from that position. Subsequent flow items are laid out as if the item had not been moved.

Absolute

Specifies absolute positioning. The element is positioned in relation to its nearest non-static ancestor.

Fixed

The item is absolutely positioned in a fixed position on the screen even as the rest of the document is scrolled.

Float and clear

The float property may have one of three values. Absolutely positioned or fixed items cannot be floated. Other elements normally flow around floated items, unless they are prevented from doing so by their clear property.

left

Floats to the left of the line that it would have appeared in; other items may flow around its right side

right

Floats to the right of the line that it would have appeared in; other items may flow around its left side

clear

Forces the element to appear underneath ('clear') floated elements to the left (clear:left), right (clear:right) or both sides (clear:both).

Style sheet language

A style sheet language, or style language, is a computer language that expresses the presentation of 

structured documents. One attractive feature of structured documents is that the content can be reused 

in many contexts and presented in various ways. Different style sheets can be attached to the logical 

structure to produce different presentations.

One modern style sheet language with widespread use is Cascading Style Sheets (CSS), which is used to

 style documents written in HTML, XHTML, SVG, XUL, and other markup languages.

For content in structured documents to be presented, a set of stylistic rules – describing, for example, colors, 

fonts and layout – must be applied. A collection of stylistic rules is called a style sheet. Style sheets in the 

form of written documents have a long history of use by editors and typographers to ensure consistency of 

presentation, spelling and punctuation. In electronic publishing, style sheet languages are mostly used in the 

context of visual presentation rather than spelling and punctuation.

Components

All style sheet languages offer functionality in these areas:

Syntax

A style sheet language needs a syntax in order to be expressed in a machine-readable manner. For 

example, here is a simple style sheet written in the CSS syntax:

h1 { font-size: 1.5em }

Selectors

Selectors specify which elements are to be influenced by the style rule. As such, selectors are the glue

 between the structure of the document and the stylistic rules in the style sheets. In the example above,

 the "h1" selector selects all h1 elements. More complex selectors can select elements based on, e.g., 

their context, attributes and content.

Properties

All style sheet languages have some concept of properties that can be given values to change one aspect

 of rendering an element. The "font-size" property of CSS is used in the above example. Common style 

sheet languages typically have around 50 properties to describe the presentation of documents.

Values and units

Properties change the rendering of an element by being assigned a certain value. The value can be a 

string, a keyword, a number, or a number with a unit identifier. Also, values can be lists or expressions

 involving several of the aforementioned values. A typical value in a visual style sheet is a length; for 

example, "1.5em" which consists of a number (1.5) and a unit (em). The "em" value in CSS refers to the 

font size of the surrounding text. Common style sheet languages have around ten different units.

Value propagation mechanism

To avoid having to specify explicitly all values for all properties on all elements, style sheet languages 

have mechanisms to propagate values automatically. The main benefit of value propagation is less-verbose

 style sheets. In the example above, only the font size is specified; other values will be found through value 

propagation mechanisms. Inheritance, initial values and cascading are examples of value propagation 

mechanisms.

Formatting model

All style sheet languages support some kind of formatting model. Most style sheet languages have a

 visual formatting model that describes, in some detail, how text and other content is laid out in the final 

presentation. For example, the CSS formatting model specifies that block-level elements (of which "h1" is 

an example) extends to fill the width of the parent element. Some style sheet languages also have an

 aural formatting model.

Document Style Semantics and Specification Language

From Wikipedia, the free encyclopedia

Document Style Semantics and Specification Language (DSSSL) is a computer language for specifying 

stylesheets for SGML documents, based on a subset of the Scheme programming language. It is specified by 

the standard ISO/IEC 10179:1996. It was developed by ISO/IEC JTC1/SC34 (ISO/IEC Joint Technical Committee 1,

 Subcommittee 34 - Document description and processing languages).

SGML contains information in a machine-readable but not very human-readable format. A "stylesheet" is used to

 present the information stored in SGML in a more pleasing or accessible way. DSSSL can convert to a wide range

 of formats, including RTF, HTML, and LaTeX.

Although compatible with any SGML, DSSSL is most often used with DocBook.

With the appearance of XML as an alternative to SGML, XML's associated stylesheet language XSL was also

 widely and rapidly adopted, from around 1999. Although DSSSL continued in use within the shrinking SGML field,

 XSL was very soon in use more extensively, and by more coders, than DSSSL had ever achieved. This was

 emphasised when previous SGML strongholds such as DocBook converted from SGML to XML, and also 

converted their favoured stylesheet language from DSSSL to XSL.

DSSSL was thought to be too complex for the World Wide Web and the World Wide Web Consortium thought 

about creating a DSSSL-Lite.

Extensible Stylesheet Language (XSL) is used to refer to a family of languages used to transform and render 

XML documents.

Historically, the XSL Working Group in W3C produced a draft specification under the name XSL, which eventually

 split into three parts:

1. XSL Transformation (XSLT): is an XML language for transforming XML documents
2. XSL Formatting Objects (XSL-FO): an XML language for specifying the visual formatting of an XML
3.  document
4. the XML Path Language (XPath): a non-XML language used by XSLT, and also available for use in non-XSLT 
5. contexts, for addressing the parts of an XML document.

As a result, the term XSL is now used with a number of different meanings:

• Sometimes it refers to XSLT: this usage is best avoided. However, "xsl" is used both as the conventional 
• namespace prefix for the XSLT namespace, and as the conventional filename suffix for files containing 
• XSLT stylesheet modules
• Sometimes it refers to XSL-FO: this usage can be justified by the fact that the XSL-FO specification carries 
• the title Extensible Stylesheet Language (XSL); however, the term XSL-FO is less likely to be misunderstood
• Sometimes it refers to both languages considered together, or to the working group that develops both
•  languages
• Sometimes, especially in the Microsoft world, it refers to a now-obsolete variant of XSLT developed and 
• shipped by Microsoft as part of MSXML before the W3C specification was finalized

This article is concerned with the various usages of the term XSL: for details of the various languages 

embraced by the term, see the relevant article.

History

XSL began as an attempt to bring the functionality of DSSSL, particularly in the area of print and high-end

 typesetting, to XML.

In response to a submission from Arbortext, Inso, and Microsoft,a W3C working group on XSL started operating

 in December 1997, with Sharon Adler and Steve Zilles as co-chairs, with James Clark acting as editor (and 

unofficially as chief designer), and Chris Lilley as the W3C staff contact. The group released a first public Working

 Draft on 18 August 1998. XSLT and XPath became W3C Recommendations on 16 November 1999 and XSL-FO

 reached Recommendation status on 15 October 2001.

[edit]"XSL" in Microsoft products

Microsoft's MSXML, first released in March 1999, contained an incomplete implementation of the December

 1998 transformation language published in the W3C XSL Working Draft. Microsoft documentation used the term 

"XSL" to refer to this language as implemented in MSXML, including MSXML-specific extensions and omissions. 

Subsequently, when MSXML was updated to support the final W3C XSLT 1.0 Recommendation, Microsoft 

documentation referred to the obsolete dialect as "XSL" and to the new language as "XSLT". Other commentators 

follow the lead of Michael Kay in referring to the older language as WD-xsl. Current versions of MSXML

 (as of 2009) continue to support the obsolete dialect, but no longer mention it in the documentation.

Since the mid-2000 release of MSXML 3.0, MSXML has had complete support for both XSLT 1.0 alongside the

 older dialect. MSXML 3.0 became the default XML services library ofInternet Explorer (IE) upon the release of 

IE 6.0 in August 2001. Older versions of IE could use MSXML 3.0 only with a custom install in "replace mode".

[edit]The XSL family

[edit]XSL Transformations

XSL Transformations (XSLT) currently has many implementations available. Several web browsers, including 

Internet Explorer (using the MSXML engine), Opera (native engine) andSafari, all support transformation of XML 

to HTML (or other languages) through XSLT. Other notable implementations include Saxon and Xalan.

Support in Firefox, Mozilla, and Netscape (all using the TransforMiiX engine) is incomplete. Support of 

disable-output-escaping does not work which is why HTML Fragments are not rendered properly. This bug is

 known since 2001 .

[edit]XSL Formatting Objects

Support for XSL Formatting Objects is available in a number of products:

• the XEP package from RenderX has near 100% support for XSL-FO 1.0
• XSLFormatter from Antenna Hou also has near 100% support for the XSL-FO 1.0 specification and has 
• 100% support for all new features within the XSL-FO 1.1 specification
• XINC from Lunasil has a great amount of support for the XSL-FO 1.0 specification
• FOP from the Apache project can render a portion of the XSL formatting objects 1.0 specification to PDF
• Xml2PDF Server 2007 from AltSoft has near 100% support for the XSL-FO 1.1

These products support output in a number of file formats, to varying degrees:

• Portable Document Format
• PostScript
• SVG
• MIF
• PCL
• text files

XPath

XML Path Language (XPath), itself part of the XSL family, functions within XSLT as a means of navigating an 

XML document.

Another W3C project, XQuery, aims to provide similar capabilities for querying XML documents using XPath.

JavaScript Style Sheets (JSSS) was a stylesheet language technology proposed by Netscape Communication

 Corporation in 1996 to provide facilities for defining the presentation of webpages. It was an alternative to the 

Cascading Style Sheets (CSS) technology. Although Netscape submitted it to the World Wide Web Consortium 

(W3C), the technology was never accepted as a formal standard and it never gained much acceptance in the 

market. Only Netscape Communicator 4 supported JSSS, with the rivalInternet Explorer web browser choosing

 not to implement the technology. Soon after Netscape Communicator's release in 1997, Netscape stopped

 promoting JSSS, instead focusing on the rival CSS standard, which was also supported by Internet Explorer 

and had much wider industry acceptance. The follow-up to Netscape Communicator, Netscape 6

 (released in 2000), dropped support for JSSS. It now remains little more than a historical footnote, with many 

Web developers not even being aware of its existence. The proposed standard was not finished.

Using JavaScript code as a stylesheet, JSSS styles individual element by modifying properties of the document.

tags object. For example, the CSS: