w3c's structured standard languages are "XHTML" and "XML": 1. XHTML is a mixture of HTML and XML, inheriting the rich markup of HTML and adopting the grammatical rules of XML; 2. XML is a markup language used to describe data and allows data exchange and processing between different systems.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

W3C's structured standard languages mainly include XHTML and XML.

1. XHTML (Extensible HyperText Markup Language) is a mixture of HTML and XML. It inherits the rich markup of HTML and adopts the syntax rules of XML. Therefore, XHTML can not only display pages as HTML, but also be crawled and indexed by search engines.

2. XML (Extensible Markup Language) is a markup language used to describe data, which can exchange and process data between different systems. The syntax rules of XML are more flexible and powerful than HTML. It can be used to create various customized tags and structures to better describe and organize data.

The following is an example of XHTML:

     
  
欢迎来到我的网站！
 
这是一个段落。
  

In this example, we use the XHTML DOCTYPE declaration to specify the document type and use the XHTML namespace to define the root element of the document. At the same time, we also use the XHTML meta tag to specify the character encoding of the document.

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