What is XML?
XML stands for Extensible Markup Language.
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XML, also called Extensible Markup Language, is used to encode documents to a format that is readable by both human and machine users. XML is similar to HTML, or HyperText Markup Language, but there are significant differences.
Extensible Markup Language
HTML and XML are both languages derived from the original Standard Generalized Markup Language (SGML) developed by Tim Berners-Lee. XML is a more simplified version of SGML. It is "extensible" because the markup symbols, or tags, are unlimited, whereas in HTML, tags are predefined.
HTML tags define the content in terms of how it is displayed (e.g., <b></b> to bold text, <i></i> to italicize text, <u></u> to underline text, etc.). HTML is a very stable and constant format for Web design, because the markup means the same thing everywhere. However, the main drawback of SGML and HTML is that you can’t change how an application like an Internet browser interprets this information. The Document Type Definition (DTD) exists within browsers to interpret what should happen when you type text or HTML. Altering a letter’s size, font and color likewise affect the DTD’s interpretation of text.
XML, on the other hand, allows you to create customized tags that define the content in terms of what data are being described. Tags such as <name></name> and <address></address> would indicate that the information that is enclosed within that tag is a person's name and address.
XHTML, or Extensible HyperText Markup Language, is a combination of XML and HTML that uses standard tags but also allows designers to define their own.
Uses for XML
XML is used in a variety of ways. It allows designers to create interactive pages and makes e-commerce applications more intuitive. It provides a common vehicle for exchanging data, making it easier for applications and devices to store and display data. XML sets rules for constructing Internet media types, such as music and video. For example, your Internet browser is able to understand when you’re downloading a video as an MP4 file because of XML.