What is XML?

Just like HTML, XML (Extensible Markup Language) is a markup language. It also relies on tags that describe certain rules and application processing tools that can read these tags to play its powerful functions. This can also be seen from the naming of XML.

"The correct title about this specification, that is, the correct full name of XML, should be Extensible Markup Language, which is just a spelling mistake. However, the abbreviation of XML is not only correct now, but also the official name of extensible markup language, just as it is in the title of this specification.

This name and abbreviation were first proposed by James Clark, and other alternative names include MGML (Miniature generalized markup language). Magma (Micro-architecture of Universal Markup Application), Standard Markup Language and Slim (Structured Language of Internet Markup).

-Extensible Markup Language (XML) 1.0 specification, annotated version. "

From the initial naming of XML, we can see that the core of XML is tag in the final analysis. However, as a markup language, XML is much more powerful than HTML.

As the name implies, the powerful function of XML comes from "X". In other words, XML is not only a markup language, but also an extensible markup language. Unlike HTML, XML does not provide a set of predefined tags, but is a standard. With this standard, you can define your own new markup language according to your actual needs and specify a set of unique tags for your markup language. To be precise, XML is a source markup language, which allows you to formulate various markup languages according to the rules it provides. This is also the initial goal of XML language.

"The goal of XML is:

XML should be available directly on the Internet (* as easy to use as HTML).

XML should support various applications (* including not only browsing, but also content analysis).

XML should be compatible with SGML (SGML is the direct pioneer of XML, as will be mentioned later).

Applications that handle XML files should be easy to write (graduate students in computer science should take two weeks).

The number of optional features in XML should be reduced to a minimum, preferably none (* optional features often cause confusion).

XML documents should be legible and clear (* Unlike HTML, reading without a browser is a test of your willpower and patience).

It should be convenient and quick to design a new markup language with XML (without going through the tedious procedure of standard formulation).

The markup language of XML design should be formal and concise (otherwise, how can it be easy to write and read? )。

XML files should be easy to compile (think about how terrible it is to write HTML in Notepad).

Simplicity of XML tags is not important (you don't have to go to great lengths to reduce tags).

-Extensible Markup Language (XML) 1.0 specification, annotated version. "

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