XHTML introductory learning tutorial: Web page Head and DTD_HTML/Xhtml_Web page production

Although head and DTD are not displayed on the page, they are important elements of the web page. Why does it go wrong?
In the previous section, we got an error message when we checked our web page, but we wrote it in accordance with XHTML standards throughout the production process of the web page. In fact, the problem lies in the "head" of the web page. Let's solve this problem below. section
In the previous tutorial, except for the , which is the content displayed on the page. So what does the part in XHTML do? In fact, in the section, we can add a lot of information that the browser can "see". Below we introduce some commonly used tags in the head part.
Note: Most of the tags and attributes in this section are difficult to remember. In fact, they are automatically generated when we use web page creation software to create web pages. The purpose of this section is to understand the meaning of these tags so that you can make some manual modifications when necessary. Now open our "index.html" and insert the following code between :
1.
This code tells the browser that our web page uses gb2312 Chinese character encoding. The absence of this information is one of the reasons for the problem during the last inspection.
2.