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About Dhtml Introduction Dynamic HyerText Markup Language (DHTML) is a combination of Web development technologies used to create dynamically changing websites. Web pages may include animation, dynamic menus and text effects. The technologies used include a combination of HTML, JavaScript or VB Script, CSS and the document object model (DOM). There are four parts to DHTML: Document Object Model (DOM) (definition) Scripts Cascading Style Sheets (CSS) XHTML DOM The DOM is what allows you to access any part of your Web page to change it with DHTML. Every part of a Web page is specified by the DOM and using its consistent naming conventions you can access them and change their properties. With the Document Object Model, programmers can build documents, navigate their structure, and add, modify, or delete elements and content. Anything found in an HTML or XML document can be accessed, changed, deleted, or added using the Document Object Model, with a few exceptions - in particular, the DOM interfaces for the XML internal and external subsets have not yet been specified. For example: <TABLE> <TBODY> <TR> <TD>Shady Grove</TD> <TD>Aeolian</TD> </TR> <TR> <TD>Over the River, Charlie</TD> <TD>Dorian</TD> </TR> </TBODY> </TABLE> A graphical representation of the DOM of the example table is: Scripts Scripts written in either JavaScript or ActiveX are the two most common scripting languages used to activate DHTML. You use a scripting language to control the objects specified in the DOM. JavaScript is an object-oriented language with prototypal inheritance. The language supports several built-in objects, and programmers can create or delete their own objects. Prototypal inheritance makes JavaScript very different from other popular programming languages such as C++, C#, or Java featuring classes and classical inheritance. JavaScript does not have classes in the C++ or Java sense. In JavaScript, objects can inherit properties directly from each other, forming the object prototype chain. ActiveX is a set of object-oriented programming (OOP) technologies and tools that Microsoft developed for Internet Explorer to facilitate rich media playback. Essentially, Internet Explorer uses ActiveX to load other software applications in the browser. One of the main advantages of ActiveX components is that they can be re-used by many applications (referred to as component containers). Unfortunately, that also means that the component can be re-used by an attacker to run malicious code and gain access to critical files. Cascading Style Sheets CSS is used in DHTML to control the look and feel of the Web page. Style sheets define the colors and fonts of text, the background colors and images, and the placement of objects on the page. Using scripting and the DOM, you can change the style of various elements. a cascading style sheet consists of ASCII text instructions telling the browser how it can format the document that is being loaded. The CSS instructions can be placed in the web page itself, or it can be placed in a separate document which is linked to the web page. The simplest way to explain a cascading style sheet is to give an example of one. Take the following code, for example, inserted in the HEAD section of a web page. <style type="text/css"> body { background-color: white ; color: black ; font-family: Arial, Helvetica, sans-serif ; } </style> XHTML XHTML or HTML 4.x is used to create the page itself and build the elements for the CSS and the DOM to work on. There is nothing special about XHTML for DHTML - but having valid XHTML is even more important, as there are more things working from it than just the browser. Html vs xhtml vs xml HTML is the HyperText Markup Language, which is designed to create structured documents and provide for semantic meaning behind the documents. HTML5 is the next version of the HTML specification. XML is the Extensible Markup Language, which provides rules for creating, structuring, and encoding documents. You often see XML being used to store data and to allow for communication between applications. It's programming language-agnostic - all of the major programming languages provide mechanisms for reading and writing XML documents, either as part of the core or in external libraries. XHTML is an XML-based HTML. It serves the same function as HTML, but with the same rules as XML documents. These rules deal with the structure of the markup. Features of DHTML Dynamic content, which allows the user to dynamically change Web page content Dynamic positioning of Web page elements Dynamic style, which allows the user to change the Web page’s color, font, size or content. Can be used to create animations, games, applications, provide new ways of navigating through web sites. DHTML use low-bandwidth effect which enhance web page functionality. Dynamic building of web pages is simple as no plug-in is required. Facilitates the usage of events, methods and properties and code reuse.