Detailed explanation of the difference between html and xhtml-HTML Tutorial-php.cn

Today I will give you a detailed introduction to two concepts, the similarities and differences between html and xhtml, to help you better understand front-end technology.

The main difference between html and xhtml: (will be distinguished by red in the following explanation examples)
1. XHTML elements must be nested correctly.
Example:
General html web pages can be "main content" This is not strict and is wrong in XHTML; correct in the xhtml standard It must require "main content".

2. XHTML elements must be closed.
exp:
1. An example inHEAD, " " A tag like this is feasible in html, but For the sake of xhtml standards, it is necessary to close such as " "
2. For example, if you use "

" in general html, it is often used to change the big line tag. People can just add a "

" tag to the paragraph that needs a line break, but in the XHTML CSS standard it must be like this "

Paragraph text

" means it must be preceded by " < p> This line break tag starts before the article text field and ends with the "

" tag after the text. 3. For example, many small line break tags " br " are used when making HTML pages. , many people don’t know that this tag needs to be wrapped in a closed style. For example, if you need to wrap a line after a paragraph of text, many CSS productions just add a "
" where a line wrap is needed, but let me tell you that this is also the case. It is not standard and cannot be passed during XHTML verification. It must be closed with "
"

3. The tag name must be in lowercase letters.
In previous web pages. Many tags are usually arranged in uppercase or lowercase, but for WEB standards, tags are now required to be uniform in lowercase.
exp:
In the past, many "," were all in uppercase or lowercase. Use mixed case such as "," or "," for typesetting, but XHTML requires the use of "," in lowercase.

4. The XHTML document must have a root element.
It means that any tag should be used to end it. For example,should be closed at the end of the content.
##5. For
pictures
need to add alt attribute In the past, many times when pictures were displayed on web pages, theimg tag
could be added or not. alt attribute, but now xhtml requires that the alt attribute be added, otherwise xhtml verification will prompt an error, even if the alt value is empty exp:Error

Correct

What are the benefits of adding alt? Answer: Adding alt can provide a text description for the image, allowing
search
engines to identify the content of the image, which is a good place to optimize web pages. In fact, when we usually do DIV+CSS, we pay more attention to the use and specifications of tags, and we will soon master the xhtml standard without paying special attention to it.
I believe you have mastered the methods after reading these cases. For more exciting information, please pay attention to other related articles on the php Chinese website!