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An example of CSS code, which makes up the visual and styling components of a web page. Separation of content and presentation (or separation of content and style) is the separation of concerns design principle as applied to the authoring and presentation of content. Under this principle, visual and design aspects (presentation and style) are ...
To demonstrate specificity Inheritance Inheritance is a key feature in CSS; it relies on the ancestor-descendant relationship to operate. Inheritance is the mechanism by which properties are applied not only to a specified element but also to its descendants. Inheritance relies on the document tree, which is the hierarchy of XHTML elements in a page based on nesting. Descendant elements may ...
However, the SGML concept of generalized markup is based on elements (nested annotated ranges with attributes) rather than merely print effects, with separate structure and markup. HTML has been progressively moved in this direction with CSS. Berners-Lee considered HTML to be an application of SGML.
HTML can embed programs written in a scripting language such as JavaScript, which affects the behaviour and content of web pages. Inclusion of CSS defines the look and layout of content. The World Wide Web Consortium (W3C), maintainer of both the HTML and the CSS standards, has encouraged the use of CSS over explicit presentational HTML since 1997.
The core element is a text file written in the HyperText Markup Language (HTML). This specifies the content of the page, [3] including images and video. Cascading Style Sheets (CSS) specify the presentation of the page. [3] CSS rules can be in separate text files or embedded within the HTML file.
At that time, Netscape proposed frames to the World Wide Web Consortium (W3C) for inclusion in the HTML 3.0 standard. [3] Frames were used to display and navigate early online magazines and web apps, such as webmail services and web chat sites.
While the W3C and other HTML and XHTML validators will assess pages coded in those formats, a separate validator like the W3C CSS validator can check that there are no errors in the associated Cascading Style Sheet. CSS validators apply current CSS standards to referenced CSS documents. [7]
CSS2 in May 1998 (later revised in CSS 2.1 and CSS 2.2) extended CSS1 with facilities for positioning and table layout. The preference for using HTML tables rather than CSS to control the layout of whole web pages was due to several reasons: the desire of content publishers to replicate their existing corporate design elements on their web site;