Style sheet (web development)

>> Wednesday, May 13, 2009

Web style sheets are a form of separation of presentation and content for web design in which the markup (i.e., HTML or XHTML) of a webpage 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 language such as CSS or XSL. 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.
Benefits
Separation of style and content has many benefits, but has only become practical in recent years due to improvements in popular web browsers' 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, Mozilla Firefox, Opera, Safari, etc.).
Sites using CSS "degrade gracefully" 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 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.

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Comparison of stylesheet languages

The two primary stylesheet languages are Cascading Style Sheets (CSS) and the Extensible Stylesheet Language (XSL). While they are both called stylesheet languages, they have very different purposes and ways of going about their tasks.

Cascading Style Sheets
CSS is designed around styling HTML and XML (including XHTML) documents. It was created for that purpose. It uses a special, non-XML syntax for defining the styling information for the various elements of the document that it styles.
CSS, as of version 2.1, is best used for styling documents that are to be shown on "screen media". That is, media displayed as a single page (possibly with hyperlinks) that has a fixed horizontal width but a virtually unlimited vertical height. Scrolling is often the method of choice for viewing parts of screen media. This is in contrast to "paged media", which has multiple pages, each with specific fixed horizontal and vertical dimensions. Styling paged media involves a variety of complexities that screen media does not. Since CSS was designed originally for screen media, its paged facilities are lacking.
CSS version 3.0 provides new features that allow CSS to more adequately style documents for paged display.
Extensible Stylesheet Language
XSL has evolved drastically from its initial design into something very different from its original purpose. The original idea for XSL was to create an XML-based styling language directed towards paged display media. The mechanism they used to accomplish this task was to divide the process into two distinct steps.
First, the XML document would be transformed into an intermediate form. The process for performing this transformation would be governed by the XSL stylesheet, as defined by the XSL specification. The result of this transformation would be an XML document in an intermediate language, known as XSL-FO (also defined by the XSL specification).
However, in the process of designing the transformation step, it was realized that a generic XML transformation language would be useful for more than merely creating a presentation of an XML document. As such, a new working group was split off from the XSL working group, and the XSL Transformations (XSLT) language became something that was considered separate from the styling information of the XSL-FO document. Even that split was expanded when XPath became its own separate specification, though still strongly tied to XSLT.
The combination of XSLT and XSL-FO creates a powerful styling language, though much more complex than CSS. XSLT is a Turing complete language, while CSS is not; this demonstrates a degree of power and flexibility not found in CSS. Additionally, XSLT is capable of creating content, such as automatically creating a table of contents just from chapters in a book, or removing/selecting content, such as only generating a glossary from a book. XSLT version 1.0 with the EXSLT extensions, or XSLT version 2.0 is capable of generating multiple documents as well, such as dividing the chapters in a book into their own individual pages. By contrast, a CSS can only selectively remove content by not displaying it.
XSL-FO is unlike CSS in that the XSL-FO document stands alone. CSS modifies a document that attached to it, while the XSL-FO document (the result of the transformation by XSLT of the original document) contains all of the content to be presented in a purely presentational format. It has a wide range of specification options with regard to paged formatting and higher-quality typesetting. But it does not specify the pages themselves. The XSL-FO document must be passed through an XSL-FO processor utility that generates the final paged media, much like HTML+CSS must pass through a web browser to be displayed in its formatted state.
The complexity of XSL-FO is a problem, largely because implementing an FO processor is very difficult. CSS implementations in web browsers are still not entirely compatible with one another, and it is much simpler than writing an FO processor. However, for richly specified paged media, such complexity is ultimately required in order to be able to solve various typesetting problems.

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Dreamweaver

Adobe Dreamweaver (formerly Macromedia Dreamweaver) is a web development application originally created by Macromedia, and is now developed by Adobe Systems, which acquired Macromedia in 2005.
Dreamweaver is available for both Mac and Windows operating systems. Recent versions have incorporated support for web technologies such as CSS, JavaScript, and various server-side scripting languages and frameworks including ASP, ColdFusion, and PHP.
Features
Although a hybrid WYSIWYG and code-based web design and development application, Dreamweaver's WYSIWYG mode can hide the HTML code details of pages from the user, making it possible for non-coders to create web pages and sites. One criticism of this approach is that it has the potential to produce HTML pages whose file size and amount of HTML code is larger than an optimally hand-coded page would be, which can cause web browsers to perform poorly. This can be particularly true because the application makes it very easy to create table-based layouts. In addition, some web site developers have criticized Dreamweaver in the past for producing code that often does not comply with W3C standards, though recent versions have been more compliant. Dreamweaver 8.0 performed poorly on the Acid2 Test, developed by the Web Standards Project. However, Adobe has focused on support for standards-based layout in recent and current versions of the application, including the ability to convert tables to layers.
Dreamweaver allows users to preview websites in locally-installed web browsers. It also has site management tools, such as FTP/SFTP and WebDAV file transfer and synchronization features, the ability to find and replace lines of text or code by search terms and regular expressions across the entire site, and a templating feature that allows single-source update of shared code and layout across entire sites without server-side includes or scripting. The behaviours panel also enables use of basic JavaScript without any coding knowledge, and integration with Adobe's Spry AJAX framework offers easy access to dynamically-generated content and interfaces.
Dreamweaver can utilize third-party "Extensions" to enable and extend core functionality of the application, which any web developer can write (largely in HTML and JavaScript). Dreamweaver is supported by a large community of extension developers who make extensions available (both commercial and free) for most web development tasks from simple rollover effects to full-featured shopping carts.
Like other HTML editors, Dreamweaver edits files locally, then uploads all edited files to the remote web server using FTP, SFTP, or WebDAV. Dreamweaver CS4 now supports the Subversion (SVN) version control system.
Syntax highlighting
As of version 6, Dreamweaver supports syntax highlighting for the following languages out of the box:
• ActionScript
• Active Server Pages (ASP).
• ASP.NET
• C#
• Cascading Style Sheets (CSS)
• ColdFusion
• EDML
• Extensible HyperText Markup Language (XHTML)
• Extensible Markup Language (XML)
• Extensible Stylesheet Language Transformations (XSLT)
• HyperText Markup Language (HTML)
• Java
• JavaScript
• JavaServer Pages (JSP)
• PHP: Hypertext Preprocessor (PHP)
• Visual Basic (VB)
• Visual Basic Script Edition (VBScript)
• Wireless Markup Language (WML)
It is also possible to add your own language syntax highlighting to its repertoire.
In addition, code completion is available for many of these languages.
Version history
CS3 Icon
Provider Major Version Minor/Alternate Name Release date Notes
Macromedia 1.0 1.0 December 1997 Initial release
1.2 March 1998
2.0 2.0 December 1998
3.0 3.0 December 1999
UltraDev 1.0 June 1999
4.0 4.0 December 2000
UltraDev 4.0 December 2000
6.0 MX May 29, 2002
7.0 MX 2004 September 10, 2003
8.0 [1]
8.0 September 13, 2005
Adobe 9.0 CS3
April 16, 2007 Replaced Adobe GoLive in the Creative Suite series
10.0 CS4
September 23, 2008

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Cascading Style Sheets

Cascading Style Sheets (CSS) is a style sheet language used to describe the presentation (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 be applied to any kind of XML document, including 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 colors, fonts, and layout. 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. While the author of a document typically links that document to a CSS stylesheet, readers can use a different stylesheet, 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) text/css is registered for use with CSS by RFC 231
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 semicolon-separated declarations in braces. Each declaration itself consists of a property, a colon (:), a value, then a semi-colon (;)
In CSS, selectors are used to declare which elements a style applies to, a kind of match expression. Selectors may apply to all elements of a specific type, or only those elements which match a certain attribute; elements may be matched depending on how they are placed relative to each other in the markup code, or on how they are nested within the document object model.
In addition to these, a set of pseudo-classes can be used to define further behavior. Probably the best-known of these is :hover, which applies a style 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. Other pseudo-classes and pseudo-elements are, for example, :first-line, :visited or :before. A special pseudo-class is :lang(c), "c".
A pseudo-class selects entire 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 other ways too, especially in CSS 2.1, to achieve greater specificity and flexibility
Use of CSS
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 a separate stylesheet resulting in considerably simpler HTML markup.
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 emphasis for these elements is presentational.
Prior to CSS, document authors who wanted to assign such typographic characteristics to, say, all h2 headings had to use the HTML font and other presentational elements for each occurrence of that heading type. The additional presentational markup in the HTML made documents more complex, and generally more difficult to maintain. In CSS, presentation is separated from structure. In print, CSS can define color, font, text alignment, size, borders, spacing, layout and many other typographic characteristics. It 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 now considers the advantages of CSS for defining all aspects of the presentation of HTML pages to be superior to other methods. It has therefore deprecated the use of all the original presentational HTML markup.
Sources
CSS information can be provided by various sources. CSS style information can be either attached as a separate document or embedded in the 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.
• Author styles (style information provided by the web page author), in the form of
o external stylesheets, i.e. a separate CSS-file referenced from the document
o embedded style, blocks of CSS information inside the HTML document itself
o inline styles, inside the HTML document, style information on a single element, specified using the "style" attribute.
• User style
o a local CSS-file specified by the user using options in the web browser, and acting as an override, to be applied to all documents.
• User agent style
o the default style sheet applied by the user agent, e.g. the browser's default presentation of elements.
One of the goals of CSS is also to allow users a greater degree of control over presentation; those who find the red italic headings difficult to read may apply other style sheets to the document. Depending on their browser and the web site, a user may choose from various stylesheets provided by the designers, may remove all added style and view the site using their browser's default styling or may perhaps override just the red italic heading style without altering other attributes.
File highlightheaders.css containing:
h1 { color: white; background: orange !important; }
h2 { color: white; background: green !important; }
Such a file is stored locally and is applicable if that has been specified in the browser options. "!important" means that it prevails over the author specifications.
History
Style sheets have existed in one form or another since the beginnings of SGML in the 1970s. 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 but at the cost of HTML becoming more complex to write and maintain. Variations in web browser implementations made consistent site appearance difficult, and users had less control over how web content was displayed.
To improve the capabilities of web presentation, nine different style sheet languages were proposed to the W3C's 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). First, Håkon Wium Lie (now the CTO of Opera Software) proposed Cascading HTML Style Sheets (CHSS) in October 1994, a language which has some resemblance to today's CSS. Bert Bos was working on a browser called Argo which used its own style sheet language, Stream-based Style Sheet Proposal (SSP). Lie and Bos worked together to develop the CSS standard (the 'H' was removed from the name because these style sheets could 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.
Håkon's proposal was presented at the "Mosaic and the Web" conference in Chicago, Illinois in 1994, and again with Bert Bos in 1995. Around this time, the World Wide Web Consortium was being established; the W3C took an interest in the development of CSS, and 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). Håkon and Bert were the primary technical staff on this aspect of the project, with additional members, including Thomas Reardon of Microsoft, participating as well. 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
Although the CSS1 specification was completed in 1996 and Microsoft's Internet Explorer 3 was released in that year featuring some limited support for CSS, it would be 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) CSS1 support[citation needed], 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 CSS2. As of July 2008, no (finished) browser has fully implemented CSS2, 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 afflicted with 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 other quirks. 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 platforms. Some authors commonly resort to using some workarounds such as CSS hacks and CSS filters in order to obtain consistent results across web browsers and platforms.
Problems with browsers' patchy adoption of CSS along with errata in the original specification led the W3C to revise the CSS2 standard into CSS2.1, which may be regarded as something nearer to a working snapshot of current CSS support in HTML browsers. Some CSS2 properties which no browser had successfully implemented were dropped, and in a few cases, defined behaviours were changed to bring the standard into line with the predominant existing implementations. CSS2.1 became a Candidate Recommendation on February 25, 2004, but CSS2.1 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 than text/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).
Variations
CSS has various levels and profiles. Each level of CSS builds upon the last, typically adding new features and typically denoted as CSS1, CSS2, and CSS3. 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 CSS2.
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 maintains the CSS1 Recommendation.
CSS 2
CSS level 2 was developed by the W3C and published as a Recommendation in May 1998. A superset of CSS1, CSS2 includes a number of new capabilities like absolute, relative, and fixed positioning of elements, the concept of media types, support for aural style sheets and bidirectional text, and new font properties such as shadows. The W3C maintains the CSS2 Recommendation.
CSS level 2 revision 1 or CSS 2.1 fixes errors in CSS2, removes poorly-supported features and adds already-implemented browser extensions to the specification. While it was a Candidate Recommendation for several months, on June 15, 2005 it was reverted to a working draft for further review. It was returned to Candidate Recommendation status on 19 July 2007.
CSS 3
CSS level 3 is currently under development. The W3C maintains a CSS3 progress report. CSS3 is modularized and will consist of several separate Recommendations. The W3C CSS3 Roadmap provides a summary and introduction.
Browser support
A CSS filteris a coding technique that aims at hiding or showing parts of the CSS to different browsers, 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 entirely different CSS to certain browsers in order to ensure that designs are rendered as expected. Because very early web browsers were either completely incapable of handling CSS, or render 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 8 offered 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 which 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 doctype in (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 should be, and cross-browser testing remains a necessity. Other reasons for 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 KHTML engine used in KDE's Konqueror browser, and Opera's Presto layout engine - each of them is leading in different aspects of CSS. As of April 2009, Internet Explorer 8 has the most complete implementation of CSS 2.1 according to one source, scoring 99%.
Limitations
Some noted disadvantages of using "pure" CSS include:
Inconsistent browser support
Different browsers will render CSS layout differently as a result of browser bugs or lack of support for CSS features. For example Microsoft Internet Explorer, whose older versions, such as IE 6.0, implemented many CSS 2.0 properties in its own, incompatible way, misinterpreted a significant number of important properties, such as width, height, and float. Numerous so-called CSS "hacks" must be implemented to achieve consistent layout among the most popular or commonly used browsers. Pixel precise layouts can sometimes be impossible to achieve across browsers.
Selectors are unable to ascend
CSS offers no way to select a parent or ancestor of element that satisfies certain criteria. A more advanced selector scheme (such as XPath) would enable more sophisticated stylesheets. However, the major reasons for the CSS Working Group rejecting proposals for parent selectors are related to browser performance and incremental rendering issues.
One block declaration cannot explicitly inherit from another
Inheritance of styles is performed by the browser based on the containment hierarchy of DOM elements and the specificity of the rule selectors, as suggested by the section 6.4.1 of the CSS2 specification. Only the user of the blocks can refer to them by including class names into the class attribute of a DOM element.
Vertical control limitations
While horizontal placement of elements is generally easy to control, vertical placement is frequently unintuitive, convoluted, or 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 is 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 orthogonality
Multiple properties often end up doing the same job. For instance, position, display and float specify the placement model, and most of the time they cannot be combined meaningfully. A display: table-cell element cannot be floated or given position: relative, and an element with float: left should not react to changes of display. In addition, some properties are not defined in a flexible way that avoids creation of new properties. For example, you should use the "border-spacing" property on table element instead of the "margin-*" property on table cell elements. This is because according to the CSS specification, internal table elements do not have margins.
Margin collapsing
Margin collapsing is, while well-documented and useful, also complicated and is frequently not expected by authors, and no simple side-effect-free way is available to control it.
Float containment
CSS does not explicitly offer any property that would force an element to contain floats. Multiple properties offer this functionality as a side effect, but none of them are completely appropriate in all situations. As there will be an overflow when the elements, which is contained in a container, use float property. Generally, either "position: relative" or "overflow: hidden"solves this. Floats will be different according to the web browser size and resolution, but positions can not.
Lack of multiple backgrounds per element
Highly graphical designs require several background images for every element, and CSS can support only one. Therefore, developers have to choose between adding redundant wrappers around document elements, or dropping the visual effect. This is partially addressed in the working draft of the CSS3 backgrounds module, which is already supported in Safari and Konqueror.
Control of Element Shapes
CSS currently only offers rectangular shapes. Rounded corners or other shapes may require non-semantic markup. However, this is addressed in the working draft of the CSS3 backgrounds module.
Lack of Variables
CSS contains no variables. This makes it necessary to use error-prone "replace-all" techniques to change fundamental constants, such as the color scheme or various heights and widths. Server-side generation of CSS scripts, using for example PHP, can help to mitigate this problem.
Lack of column declaration
While possible in current CSS, layouts with multiple columns can be complex to implement. With the current CSS, 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 two undesired effects: 1) 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 and 2) users are often not aware that they must declare position:relative or position:absolute on any element they want to act as "the new scope". Additionally, a bug in the Firefox browser prevents one from declaring table elements as a new css scope using position:relative (one can technically do so, but numerous graphical glitches result).
Poor Layout Controls for Flexible Layouts
While new additions to CSS3 provide a stronger, more robust layout feature-set, CSS is still very much rooted as a styling language, not a layout language.
Advantages
Flexibility
By combining CSS with the functionality of a Content Management System, a considerable amount of flexibility can be programmed into content submission forms. This allows a contributor, who may not be familiar or able to understand or edit CSS or HTML code to select the layout of an article or other page they are submitting on-the-fly, in the same form. For instance, a contributor, editor or author of an article or page might be able to select the number of columns and whether or not the page or article will carry an image. This information is then passed to the Content Management System, and the program logic will evaluate the information and determine, based on a certain number of combinations, how to apply classes and IDs to the HTML elements, therefore styling and positioning them according to the pre-defined CSS for that particular layout type. When working with large-scale, complex sites, with many contributors such as news and informational sites, this advantage weighs heavily on the feasibility and maintenance of the project.
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
When CSS is used effectively, in terms of inheritance and "cascading," a global stylesheet 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 easily, simply by editing a few rules in the global stylesheet. Before CSS, this sort of maintenance was more difficult, expensive and time-consuming.
Bandwidth
A stylesheet will usually be stored in the browser cache, and can therefore be used on multiple pages without being reloaded, increasing download speeds and reducing data transfer over a network.
Page reformatting
With a simple change of one line, a different stylesheet 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 will still display the content.

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Web design

>> Wednesday, May 6, 2009

Web design is the skill of designing presentations of content (usually hypertext or hypermedia) that is delivered to an end-user through the World Wide Web, by way of a Web browser or other Web-enabled software like Internet television clients, microblogging clients and RSS readers.
The process of designing Web pages, Web sites, Web applications or multimedia for the Web may utilize multiple disciplines, such as animation, authoring, communication design, corporate identity, graphic design, human-computer interaction, information architecture, interaction design, marketing, photography, search engine optimization and typography.
Involved technologies may include (see Web development):
• Markup languages (such as XHTML and XML)
• Style sheet languages (such as CSS and XSL)
• Client-side scripting (such as JavaScript and VBScript)
• Server-side scripting (such as PHP and ASP)
• Database technologies (such as MySQL)
• Multimedia technologies (such as Flash and Silverlight)
Web pages and Web sites can be static pages, or can be programmed to be dynamic pages that automatically adapt content or visual appearance depending on a variety of factors, such as input from the end-user, input from the Webmaster or changes in the computing environment (such as the site's associated database having been modified).
With growing specialization within communication design and information technology fields, there is a strong tendency to draw a clear line between web design specifically for web pages and web development for the overall logistics of all web-based services.
History
Tim Berners-Lee published what is considered to be the first website in August 1991. Berners-Lee was the first to combine Internet communication (which had been carrying email and the Usenet for decades) with hypertext (which had also been around for decades, but limited to browsing information stored on a single computer, such as interactive CD-ROM design). Websites are written in a markup language called HTML, and early versions of HTML were very basic, only giving a website's basic structure (headings and paragraphs), and the ability to link using hypertext. This was new and different from existing forms of communication - users could easily navigate to other pages by following hyperlinks from page to page.
As the Web and web design progressed, the markup language changed to become more complex and flexible, giving the ability to add objects like images and tables to a page. Features like tables, which were originally intended to be used to display tabular information, were soon subverted for use as invisible layout devices. With the advent of Cascading Style Sheets (CSS), table-based layout is commonly regarded as outdated. Database integration technologies such as server-side scripting and design standards like W3C further changed and enhanced the way the Web is made. As times change, websites are changing the code on the inside and visual design on the outside with ever-evolving programs and utilities.
With the progression of the Web, tens of thousands of web design companies have been established around the world to serve the growing demand for such work. As with much of the information technology industry, many web design companies have been established in technology parks in the developing world as well as many Western design companies setting up offices in countries such as India, Romania, and Russia to take advantage of the relatively lower labor rates found in such countries.
Web site design
A web site is a collection of information about a particular topic or subject. Designing a web site is defined as the arrangement and creation of web pages that in turn make up a web site[citation needed]. A web page consists of information for which the web site is developed. A web site might be compared to a book, where each page of the book is a web page.
There are many aspects (design concerns) in this process, and due to the rapid development of the Internet, new aspects may emerge. For non-commercial web sites, the goals may vary depending on the desired exposure and response. For typical commercial web sites, the basic aspects of design are:
• The content: the substance, and information on the site should be relevant to the site and should target the area of the public that the website is concerned with.
• The usability: the site should be user-friendly, with the interface and navigation simple and reliable.
• The appearance: the graphics and text should include a single style that flows throughout, to show consistency. The style should be professional, appealing and relevant.
• The visibility: the site must also be easy to find via most, if not all, major search engines and advertisement media.
A web site typically consists of text and images. The first page of a web site is known as the Home page or Index. Some web sites use what is commonly called a Splash Page. Splash pages might include a welcome message, language or region selection, or disclaimer. Each web page within a web site is an HTML file which has its own URL. After each web page is created, they are typically linked together using a navigation menu composed of hyperlinks. Faster browsing speeds have led to shorter attention spans and more demanding online visitors and this has resulted in less use of Splash Pages, particularly where commercial web sites are concerned.
Once a web site is completed, it must be published or uploaded in order to be viewable to the public over the internet. This may be done using an FTP client. Once published, the web master may use a variety of techniques to increase the traffic, or hits, that the web site receives. This may include submitting the web site to a search engine such as Google or Yahoo, exchanging links with other web sites, creating affiliations with similar web sites, etc.
Multidisciplinary requirements
Web site design crosses multiple disciplines of information systems, information technology and communication design. The web site is an information system whose components are sometimes classified as front-end and back-end. The observable content (e.g. page layout, user interface, graphics, text, audio) is known as the front-end. The back-end comprises the organization and efficiency of the source code, invisible scripted functions, and the server-side components that process the output from the front-end. Depending on the size of a Web development project, it may be carried out by a multi-skilled individual (sometimes called a web master), or a project manager may oversee collaborative design between group members with specialized skills .
Issues
As in collaborative designs, there are conflicts between differing goals and methods of web site designs. These are a few of the ongoing ones.
Lack of collaboration in design
In the early stages of the web, there wasn't as much collaboration between web designs and larger advertising campaigns, customer transactions, social networking, intranets and extranets as there is now. Web pages were mainly static online brochures disconnected from the larger projects.
Many web pages are still disconnected from larger projects. Special design considerations are necessary for use within these larger projects. These design considerations are often overlooked, especially in cases where there is a lack of leadership, lack of understanding of why and technical knowledge of how to integrate, or lack of concern for the larger project in order to facilitate collaboration. This often results in unhealthy competition or compromise between departments, and less than optimal use of web pages.
Liquid versus fixed layouts
On the web the designer has no control over several factors, including the size of the browser window, the web browser used, the input devices used (mouse, touch screen, voice command, text, cell phone number pad, etc.) and the size, design, and other characteristics of the fonts users have available (installed) on their own computers.
Some designers choose to control the appearance of the elements on the screen by using specific width designations. This control may be achieved in HTML through the use of table-based design or more modern div-based design, usually enhanced (and made more flexible) with CSS. When the text, images, and layout do not vary among browsers, this is referred to as fixed-width design. Advocates of fixed-width design argue for the designers' precise control over the layout of a site and the placement of objects within pages.
Other designers choose a more liquid approach, one which arranges content flexibly on users' screens, responding to the size of their browsers' windows. For better or worse, they concede to users more control over the rendition of their work. Proponents of liquid design prefer greater compatibility with users' various choices of presentation and more efficient use of the screen space available. Liquid design can be achieved by setting the width of text blocks and page modules to a percentage of the page, or by avoiding specifying the width for these elements altogether, allowing them to expand or contract naturally in accordance with the width of the browser. It is more in keeping with the original concept of HTML, that it should specify, not the appearance of text, but its contextual function, leaving the rendition to be decided by users' various display devices.
Web page designers (of both types) must consider how their pages will appear on various screen resolutions. Sometimes the most pragmatic choice is to allow text width to vary between minimum and maximum values. This allows designers to avoid considering rare users' equipment while still taking good advantage of available screen space.
Similar to liquid layout is the optional fit to window feature with Adobe Flash content. This is a fixed layout that optimally scales the content of the page without changing the arrangement or text wrapping when the browser is resized.
Flash
Adobe Flash (formerly Macromedia Flash) is a proprietary, robust graphics animation or application development program used to create and deliver dynamic content, media (such as sound and video), and interactive applications over the web via the browser.
Many graphic artists use Flash because it gives them exact control over every part of the design, and anything can be animated and generally "jazzed up". Some application designers enjoy Flash because it lets them create applications that do not have to be refreshed or go to a new web page every time an action occurs. Flash can use embedded fonts instead of the standard fonts installed on most computers. There are many sites which forgo HTML entirely for Flash. Other sites may use Flash content combined with HTML as conservatively as gifs or jpegs would be used, but with smaller vector file sizes and the option of faster loading animations. Flash may also be used to protect content from unauthorized duplication or searching. Alternatively, small, dynamic Flash objects may be used to replace standard HTML elements (such as headers or menu links) with advanced typography not possible via regular HTML or CSS (see Scalable Inman Flash Replacement).
Flash is not a standard produced by a vendor-neutral standards organization like most of the core protocols and formats on the Internet. Flash is much more self-contained than the open HTML format as it does not integrate with web browser UI features. For example: the browsers "Back" button couldn't be used to go to a previous screen in the same Flash file, but instead a previous HTML page with a different Flash file. The browsers "Reload" button wouldn't reset just a portion of a Flash file, but instead would restart the entire Flash file as loaded when the HTML page was entered, similar to any online video. Such features would instead be included in the interface of the Flash file if needed.
Flash requires a proprietary media-playing plugin to be seen. According to a study,[2] 98% of US Web users have the Flash Player installed.[3] The percentage has remained fairly constant over the years; for example, a study conducted by NPD Research in 2002 showed that 97.8% of US Web users had the Flash player installed. Numbers vary depending on the detection scheme and research demographics.[4]
Flash detractors claim that Flash websites tend to be poorly designed, and often use confusing and non-standard user-interfaces, such as the inability to scale according to the size of the web browser, or its incompatibility with common browser features such as the back button. Up until recently, search engines have been unable to index Flash objects, which has prevented sites from having their contents easily found. This is because many search engine crawlers rely on text to index websites. It is possible to specify alternate content to be displayed for browsers that do not support Flash. Using alternate content will help search engines to understand the page, and can result in much better visibility for the page. However, the vast majority of Flash websites are not disability accessible (for screen readers, for example) or Section 508 compliant. An additional issue is that sites which commonly use alternate content for search engines to their human visitors are usually judged to be spamming search engines and are automatically banned.
The most recent incarnation of Flash's scripting language (called "ActionScript", which is an ECMA language similar to JavaScript) incorporates long-awaited usability features, such as respecting the browser's font size and allowing blind users to use screen readers. Actionscript 2.0 is an Object-Oriented language, allowing the use of CSS, XML, and the design of class-based web applications.
CSS versus tables for layout
For more details on this topic, see Tableless web design.
When Netscape Navigator 4 dominated the browser market, the popular solution available for designers to lay out a Web page was by using tables. Often even simple designs for a page would require dozens of tables nested in each other. Many web templates in Dreamweaver and other WYSIWYG editors still use this technique today. Navigator 4 didn't support CSS to a useful degree, so it simply wasn't used.
After the browser wars subsided, and the dominant browsers such as Internet Explorer became more W3C compliant, designers started turning toward CSS as an alternate means of laying out their pages. CSS proponents say that tables should be used only for tabular data, not for layout. Using CSS instead of tables also returns HTML to a semantic markup, which helps bots and search engines understand what's going on in a web page. All modern Web browsers support CSS with different degrees of limitations.
However, one of the main points against CSS is that by relying on it exclusively, control is essentially relinquished as each browser has its own quirks which result in a slightly different page display. This is especially a problem as not every browser supports the same subset of CSS rules. There are the means to apply different styles depending on which browser and version are used but incorporating these exceptions makes maintaining the style sheets more difficult as there are styles in more than one place to update.
For designers who are used to table-based layouts, developing Web sites in CSS often becomes a matter of trying to replicate what can be done with tables, leading some to find CSS design rather cumbersome due to lack of familiarity. For example, at one time it was rather difficult to produce certain design elements, such as vertical positioning, and full-length footers in a design using absolute positions. With the abundance of CSS resources available online today, though, designing with reasonable adherence to standards involves little more than applying CSS 2.1 or CSS 3 to properly structured markup.
These days most modern browsers have solved most of these quirks in CSS rendering and this has made many different CSS layouts possible. However, some people continue to use old browsers, and designers need to keep this in mind, and allow for graceful degrading of pages in older browsers. Most notable among these old browsers is Internet Explorer 6, which, according to some web designers, is becoming the new Netscape Navigator 4 — a block that holds the World Wide Web back from converting to CSS design. However, the W3 Consortium has made CSS in combination with XHTML the standard for web design.
Form versus function
Some web developers may pay more attention to how a page looks while neglecting other copywriting and search engine optimization functions such as the readability of text, the ease of navigating the site, or how easily the visitors are going to find the site. As a result, the designers may end up in disputes where some want more decorative graphics at the expense of keyword-rich text, bullet lists, and text links. Assuming a false dichotomy that form and function are mutually exclusive overlooks the possibility of integrating multiple disciplines for a collaborative and synergistic solution. In many cases form follows function. Because some graphics serve communication purposes in addition to aesthetics, how well a site works may depend on the graphic design ideas as well as the professional writing considerations.
When using a lot of graphics, a web page can load slowly, often irritating the user. This has become less of a problem as the internet has evolved with high-speed internet and the use of vector graphics. However there is still an ongoing engineering challenge to increase bandwidth and an artistic challenge to minimize the amount of graphics and their file sizes. This challenge is compounded since increased bandwidth encourages more graphics with larger file sizes.
Accessible Web design
Main article: Web accessibility
To be accessible, web pages and sites must conform to certain accessibility principles. These accessibility principles are known as the WCAG when talking about content. These can be grouped into the following main areas:
• Use semantic markup that provides a meaningful structure to the document (i.e. web page)
• Semantic markup also refers to semantically organizing the web page structure and publishing web services description accordingly so that they can be recognized by other web services on different web pages. Standards for semantic web are set by IEEE
• Use a valid markup language that conforms to a published DTD or Schema
• Provide text equivalents for any non-text components (e.g. images, multimedia)
• Use hyperlinks that make sense when read out of context. (e.g. avoid "Click Here.")
• Don't use frames
• Use CSS rather than HTML tables for layout.
• Author the page so that when the source code is read line-by-line by user agents (such as a screen readers) it remains intelligible. (Using tables for design will often result in information that is not.)
However, W3C permits an exception where tables for layout either make sense when linearized or an alternate version (perhaps linearized) is made available.
Website accessibility is also changing as it is impacted by Content Management Systems that allow changes to be made to webpages without the need of obtaining programming language knowledge.
Website planning
Before creating and uploading a website, it is important to take the time to plan exactly what is needed in the website. Thoroughly considering the audience or target market, as well as defining the purpose and deciding what content will be developed are extremely important.
Purpose
It is essential to define the purpose of the website as one of the first steps in the planning process. A purpose statement should show focus based on what the website will accomplish and what the users will get from it. A clearly defined purpose will help the rest of the planning process as the audience is identified and the content of the site is developed. Setting short and long term goals for the website will help make the purpose clear and plan for the future when expansion, modification, and improvement will take place.Goal setting practices and measurable objectives should be identified to track the progress of the site and determine success.
Audience
Defining the audience is a key step in the website planning process. The audience is the group of people who are expected to visit your website – the market being targeted. These people will be viewing the website for a specific reason and it is important to know exactly what they are looking for when they visit the site. A clearly defined purpose or goal of the site as well as an understanding of what visitors want to do or feel when they come to your site will help to identify the target audience. Upon considering who is most likely to need or use the content, a list of characteristics common to the users such as:
• Audience Characteristics
• Information Preferences
• Computer Specifications
• Web Experience
Taking into account the characteristics of the audience will allow an effective website to be created that will deliver the desired content to the target audience.
Content
Content evaluation and organization requires that the purpose of the website be clearly defined. Collecting a list of the necessary content then organizing it according to the audience's needs is a key step in website planning. In the process of gathering the content being offered, any items that do not support the defined purpose or accomplish target audience objectives should be removed. It is a good idea to test the content and purpose on a focus group and compare the offerings to the audience needs. The next step is to organize the basic information structure by categorizing the content and organizing it according to user needs. Each category should be named with a concise and descriptive title that will become a link on the website. Planning for the site's content ensures that the wants or needs of the target audience and the purpose of the site will be fulfilled.
Compatibility and restrictions
Because of the market share of modern browsers (depending on your target market), the compatibility of your website with the viewers is restricted. For instance, a website that is designed for the majority of websurfers will be limited to the use of valid XHTML 1.0 Strict or older, Cascading Style Sheets Level 1, and 1024x768 display resolution. This is because Internet Explorer is not fully W3C standards compliant with the modularity of XHTML 1.1 and the majority of CSS beyond 1. A target market of more alternative browser (e.g. Firefox, Safari and Opera) users allow for more W3C compliance and thus a greater range of options for a web designer.
Another restriction on webpage design is the use of different Image file formats. The majority of users can support GIF, JPEG, and PNG (with restrictions). Again Internet Explorer is the major restriction here, not fully supporting PNG's advanced transparency features, resulting in the GIF format still being the most widely used graphic file format for transparent images.
Many website incompatibilities go unnoticed by the designer and unreported by the users. The only way to be certain a website will work on a particular platform is to test it on that platform.
Planning documentation
Documentation is used to visually plan the site while taking into account the purpose, audience and content, to design the site structure, content and interactions that are most suitable for the website. Documentation may be considered a prototype for the website – a model which allows the website layout to be reviewed, resulting in suggested changes, improvements and/or enhancements. This review process increases the likelihood of success of the website.
The first step may involve information architecture in which the content is categorized and the information structure is formulated. The information structure is used to develop a document or visual diagram called a site map. This creates a visual of how the web pages or content will be interconnected, and may help in deciding what content will be placed on what pages.
In addition to planning the structure, the layout and interface of individual pages may be planned using a storyboard. In the process of storyboarding, a record is made of the description, purpose and title of each page in the site, and they are linked together according to the most effective and logical diagram type. Depending on the number of pages required for the website, documentation methods may include using pieces of paper and drawing lines to connect them, or creating the storyboard using computer software.
Some or all of the individual pages may be designed in greater detail as a website wireframe, a mock up model or comprehensive layout of what the page will actually look like. This is often done in a graphic program, or layout design program. The wireframe has no working functionality, only planning, though it can be used for selling ideas to other web design companies.

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