Web browser engine
An HTML renderer is a program for visualization of Hyper Text Markup Language.
HTML was called " hypertext IIRC " originally a ( structural ) description of text, a kind of rich text with hyperlink functionality, from the inventor of the World Wide Web, Tim Berners -Lee. While there are HTML attributes that describe directly the appearance of the element (such as the font size), but these are only disapproved in XHTML and newer standards and are only supported for compatibility reasons.
This reflects the fact that HTML should not specify how a document is to be displayed. This HTML is so flexible that it can be displayed eg in a beamer presentation, on a computer monitor, a PDA or a black and white LCD. All these display devices have different requirements for the visual design of the content. Since HTML does not define such a design, the viewer can interpret HTML display device specific and customize the visual layout more or less freely.
The HTML renderer assigns this rather semantic- structural definition to a visual representation of the text.
This happens in almost all browsers using Cascading Style Sheets ( CSS). The style sheets contain a list of selectors ( conditions to the partial structure of the HTML document that must be met in order to apply the rules ) and rules ( attributes that are applied to the corresponding subtree associated visual representation ). By default, the browser delivers a default stylesheet that reason reformatted most of the elements. CSS is very flexible. It is possible to replace this set of rules completely per -user or per document. This representation of the variations are almost no limits.
An HTML renderer is thus part of a web browser, which assigns a more semantically oriented document structure a visual representation. A layout engine interprets the layout model, which was defined by CSS, and fills in this layout the semantically enriched by HTML text.
Operation
Parsing
The HTML document is read and its elements structured. This process is called parsing. Almost every browser uses for its own renderer. The definition of the standards for HTML Documents are determined among other things by the World Wide Web Consortium and defined. In this case, there are different standards, the syntax of the elements remains largely the same. The developer should specify using the so-called doctypes which standard is being used. If the specified standard is not fully met, the HTML document is not valid, the browser can not correctly interpret the elements and may lead to misstatement.
Generation of the Document Object Model
If the document has been read successfully, a so-called Document Object Model is created. This hierarchical structure includes information on the organization and sub-elements (children mentioned ). The Document Object Model is still relevant even after the issue since some client-side scripting languages like JavaScript can access this in order to manipulate it.
Reflow
Calculating SGML structures (such as HTML) is referred to as reflow. In this process, the basic geometry of the objects to be formatted is calculated - about the height or width of an element. Always format the objects are called frames (German border), and are not to be confused with the frames that allow you to download a HTML page to another.
List of renderers
Rendering audio data
There are also rendering audio data from HTML by a CSS specification part, with a synthetic voice when reading hypertext through CSS attributes is navigated. However rendering audio data is not implemented in the popular web browsers. Rendering audio data are only available in special application programs ( screen reader ) for blind or visually impaired people.