Introduction to .

XHTML is a new generation of HTML markup language.

• The purpose of XHTML is to replace HTML.

• XHTML tags are exactly the same as HTML.

• The syntax of XHTML is much stricter than HTML.

• XHTML Extensible Hypertext Markup Language.

XHTML writing specifications

All tags and attributes must be all lowercase

• One-sided tags must be turned off. For example:
  ——>
  

• All attribute values must be enclosed in quotation marks.

• All attributes must have values. For example:

  ---

  ——

  ---

• Tags must be nested sequentially, with the outer layer nested within the inner layer, and one layer within another. layer.

• XHTML web pages must have DTD document type definition code.

Note: I hope that when you write HTML in the future, you will try to strictly follow the XHTML writing specifications

##DTD document type definition

#The purpose of DTD document type definition: it is a verification mechanism, that is, to check whether the XHTML markup syntax you wrote is legitimate.

There are three major types of DTD:

(1) Strict DTD