What is the difference between xHTML and HTML?

All tags must be in lowercase.
In XHTML, all tags must be in lower case, and cannot be entered in case-insensitive or all tags must be in upper case. The example is as follows.
Error:
Correct:
Tags must be paired
Like

...

,...,... Tags, etc. When a tag appears, a corresponding end tag must exist, just like brackets in any programming language.
Error: Hello everyone

Is really good


Correct:

Hello everyone

Is really good

Summary:
The tag sequence must be correct. labels are enclosed in layers from the outside to the inside. Therefore, if you write div first and then h1, you must write h1 at the end and then div. As long as you remember a principle "first come first", the first pop-up label is to end later.
Error: hello
Correct: csdn
Double quotation marks are required for all attributes.
In XHTML 1.0, single quotation marks cannot be used, so double quotation marks are used throughout the process.

Error: csdn is correct: csdn5
Target = "_ blank" is not allowed"
The target attribute is completely forbidden from XHTML1.1. If you want to enable the function of opening a new window, you must rewrite it to rel = "external" and use JavaScript to achieve this effect.

Error: csdn is correct: csdn