What is the difference between xhtml and html? Shuai breaks the Guinness Book

What is the difference between xhtml and html-Shuai breaks the Guinness eXtensible HyperText Markup Language XHTML (eXtensible HyperText Markup Language) and is the first revision of HTML 4.01, it is composed of three types of HTML 4 files reorganized according to the XML1.0 standard. That is to say, XHTML is a mixture of HTML 4.01 and XML1.0.

Because XHTML1.0 is based on HTML4.01 and does not introduce any new tags or attributes (XHTML can be considered as a subset of HTML), it is similar to HTML, the syntax is more rigorous. Almost all Web browsers are compatible with XHTML while parsing HTML correctly.

For example, all tags in XHTML must be in lowercase, all tags must be closed, and each attribute must be enclosed by quotation marks.
To write
, Cannot be written
(Same as hr); used

There must be one

To end the paragraph.