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XML didn't just pop up out of thin air. It was created when the World Wide Web Consortium decided that it would be a good idea to make a version of SGML that was a little less cumbersome and designed with the World Wide Web in mind.
SGML is a language for creating other languages, just like HTML. However, it is very complex, and offers a number of features that are not useful for applications on the World Wide Web. For that reason, many people don't turn to SGML for a solution when they could.
XML is designed to help streamline SGML, the working group has taken the best features of SGML, thrown out the things that 98% of us won't ever use, and the result is XML.

The Confusion of XML
XML, HTML, and SGML are all languages that involve tags, but there are some important differences. SGML is a very complicated, powerful language, which is one of the reasons that it has never received the same press that XML has recently received.
HTML is different because it has a predefined set of tags. You can look up all the tags.You can look up all the tags in HTML and use them, but you can't add your own tags to HTML. That's what make it a standard.

That's where things start to get complicated. XML shares many features with SGML, including the ability to create your own tags, but it is easier to understand than SGML, HTML is great for displaying content on the Web, but lacks the flexibility of XML.

XML Doesn't Define XML Tags
As we mentioned, XML does not have any predefined tags. That's why it is extensible. You can create tags for your specific needs, rather than being limited to a set of predefined tags. HTML, however, does contain a number of tags, which have been defined by the World Wide Web Consortium (W3C). For example, the W3C has defined a tag for bold, which we've used in the previous examples, . In fact. HTML contains a number

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