What is the difference between xhtml and html

Difference: 1. XHTML must be nested correctly, html does not need to; 2. XHTML elements must be closed, html does not need to; 3. XHTML tag names must use lowercase letters, html does not need to; 4. XHTML The document must have a root element; 5. XHTML needs to add alt attributes to images, but html does not.

The operating environment of this tutorial: Windows 7 system, HTML5 version, Dell G3 computer.

HTML and XHTML

Extensible Hypertext Markup Language Language) as a standard redefined for XML applications.

There are two syntaxes defined in the HTML5 standard (HTML 4.01 and XHTML 1). This standard can be used to XHTML by defining a special DOCTYPE tag, but not many browsers implement this standard. So in the end the HTML5 standard overturned this decision.

You can indicate the choice of syntax by changing the MIME type (Content-Type included in the HTTP request): if you need to use XHTML, the MIME type should be application/xhtml xml, otherwise the MIME type should be text/html Use XHTML.

The appropriate MIME type must be present in the Content-Type in the HTTP request. If you only write the MIME type in the HTML tag, such as , it will still be executed as text/html.

The difference between xhtml and html

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 xhtml The standard must require such "main content".

2. XHTML elements must be closed

exp:

An example in HEAD, " " Tags like this are feasible in HTML, but for the sake of xhtml standards, they must be closed such as " "

For example, when using the "

" line break tag in general HTML, many people just add a "

" tag to the paragraph that needs to be broken, but in the XHTML CSS standard, it must be like this " < ;p>Paragraph text

” means that it must start with the line break tag “

” before the article text field, and end with the “

” tag after the paragraph text.

For example, many people use the small line break tag "br" when making html pages. Many people don't know that this tag needs to be wrapped in a closed style. For example: after a paragraph of text, a line break is required. Many CSS productions require line breaks. It would be nice to add a "
" here, but let me tell you that this is also non-standard. It will not pass during XHTML verification and must be closed with "
".

3. Tag names must use lowercase letters

In previous web pages, many tags were usually arranged in uppercase or lowercase letters, but for the sake of WEB standards, tags now require uniform lowercase letters. .

exp:

In the past, many ", " were used in uppercase or mixed case, such as ", " or " , ” typesetting, but XHTML unified requirements need to use “ , ” in lowercase.

4. XHTML documents must have root elements

It means that as soon as a tag starts, it must end with a tag. For example, when starts, it must be closed with at the end of the content.

5 , For pictures, you need to add the alt attribute

In the past, you could add or not add the alt attribute to the img tag of the image displayed on the web page, but now xhtml requires that the alt attribute must be added, otherwise the xhtml verification will prompt Error, even if the value of alt is empty.

exp:

Error<img src="image address" />

Correct<img src="Picture address" alt="Picture description" />

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.

Recommended tutorial: "html video tutorial"

The above is the detailed content of What is the difference between xhtml and html. For more information, please follow other related articles on the PHP Chinese website!