What are the differences between xHTML and HTML tags?

All tags must be lowercase

In XHTML, all tags must be lowercase. You cannot mix uppercase and lowercase letters, nor can you use all uppercase letters. The following is an example.
Error: <Head></Head><Body></Body>
Correct: <head></head><body></body>

Tags must be in pairs

Like <p>...</p>, <a>...</a>, <div>...</div> tags, when a tag appears, there must be a corresponding end tag, both of which are indispensable, just like brackets in any programming language.
Wrong: Hello everyone <p> is the real good thing Correct: <p>Hello everyone</p><p> is the real good thing</p>

Summarize:

The order of tags must be correct. Tags are wrapped from the outside to the inside, layer by layer. So if you write div first and then h1, you should write h1 first and then div at the end. Just remember the principle of "first in, last out", the tag that pops up first should end last.
error: <div><h1>hello</div></h1>
Correct: <div><h1>csdn</h1></div>

All attributes must be enclosed in double quotes.

XHTML 1.0 stipulates that even single quotes cannot be used, so double quotes must be used throughout.
error：<div style=font-size:11px>csdn</div>
Correct: <div style="font-size:11px">csdn</div

target="_blank" is not allowed

Starting from XHTML1.1, the target attribute is completely prohibited. If you want to have the function of opening a new window, you must rewrite it as rel="external" and use JavaScript to achieve this effect.
error：<a href="http://blog.mukispace.com" target="_blank">csdn</a>
Correct: <a href="http://blog.mukispace.com" rel="external">csdn</a> stick out your tongue

<<: N ways to vertically center a div with single/multi-line text (unknown height/fixed height)

>>: The docker-maven-plugin plugin cannot pull the corresponding jar package