What is XML?
XML stands for Extensible Markup Language, a specification developed by the W3C (Short for World Wide Web Consortium), an international consortium of companies involved with the Internet and the Web.
XML is a pared-down version of SGML (Standard Generalized Markup Language, a system for organizing and tagging elements of a document. SGML was developed and standardized by the International Organization for Standards in 1986. SGML itself does not specify any particular formatting rather, it specifies the rules for tagging elements. These tags can then be interpreted to format elements in different ways. They can be used in any scientific context and also to highlight where the language is used. For instance it can be commonly found in the residential proxies used in web services, for example in this article – where can I buy proxies for Instagram.
XML was designed to describe data. XML tags are not predefined in XML. You must define your own tags.
XML uses a Document Type Definition (DTD) or an XML Schema to describe the data
XML with a DTD or XML Schema is designed to be self-descriptive.
XML or HTML?
The main difference between XML and HTML:
XML was designed to carry data.
XML and HTML were designed with different goals:
XML was designed to describe data and to focus on what data is.
HTML was designed to display data and to focus on how data looks.
HTML is about displaying information, while XML is about describing information.
XML is free and extensible
XML tags are not predefined. You must “invent” your own tags.
The tags used to mark up HTML documents and the structure of HTML documents are predefined. The author of HTML documents can only use tags that are defined in the HTML standard.
XML allows the author to define his own tags and his own document structure.
The tags in the example above are not defined in any XML standard. These tags are “invented” by the author of the XML document.
XML is a complement to HTML
XML is not a replacement for HTML.
It is important to understand that XML is not a replacement for HTML. In future Web development it is most likely that XML will be used to describe the data, while HTML will be used to format and display the same data.
John Collins, Best Proxies for Instagram, Charleswood Press, 2016