The main difference between HTML and XHTML is in the syntax and rules of the language.
HTML (Hypertext Markup Language) is a markup language that uses a more relaxed syntax, allowing for some errors and omissions. For example, in HTML, tags do not have to be closed, and attribute values do not have to be in quotes.
XHTML (Extensible Hypertext Markup Language) is a stricter version of HTML that follows XML rules. It requires well-formed syntax, meaning that every tag must be closed and attribute values must be enclosed in quotes. XHTML documents are also required to be properly nested and have a root element.
Here's an example of HTML code:
Here's an example of the same code in XHTML:
As you can see, the main difference is in the syntax and the use of the <!DOCTYPE> declaration in XHTML.