head The contents of the element are “ Metadata ”（ Metadata ： Data that describes data ）

• Generally used to describe various information of web pages , such as Character encoding 、 Webpage title 、 Web icons

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)title Elements ： The title of the page

title Elements ： The title of the page

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)meta Elements ： Character encoding of web pages

meta The element is used for Set the character encoding of the web page , No setting or wrong setting will lead to garbled code

• Generally used UTF-8 code , It covers almost all the words in the world

stay HTML5 Before ,meta The writing of labels is also more complex

The elements listed below are mostly in head Element internal use ：

• meta

• title

• style

• link

• base

• script

• noscritpt

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)base Elements ： Set up a The default behavior of the element

base The element is used for Set all settings for the current page a The default behavior of the element ;base The elements are written in head In the elements

body Elements ： The specific content and structure of the web page

body The content in the element is what you see in the browser window , That is to say The specific content and structure of the web page

Official documents are the most authoritative references , You can see HTML5 All relevant information

• https://www.w3.org

• https://www.w3.org/standards/techs/html

HTML5 Code specification detector ：https://validator.w3.org/

h、p、strong Elements ： Text style

h The element represents The title of the page （h1 ~ h6 There is a total stipulation that 6 The title of a level ）

h Elements and SEO

h Elements contribute to the website's SEO (Search Engine Optimization) Optimize , Can promote keyword ranking

It is recommended that there be at most 1 individual h1 Elements

Misuse h Elements not only don't bring good weight to the website , At the same time, it may also be considered cheating by search engines , Finally lead to K standing

p Elements Represents a paragraph in an article （paragraph）

strong The element is used for Emphasize certain texts , Bold display effect

pre、code、br Elements ： Structural pattern

By default ,HTML Most spaces in the code are compressed by the browser

• For example, a continuous space will be compressed into 1 A space

If you want to Keep all HTML Space in the code 、 Line break , have access to pre Elements

code The element is used for Display program code

br The element is Single label , Express Forced line wrap

Character entities ： Show special symbols

HTML Some characters are reserved for special purposes , Like the less than sign <、 More than no. >

To display these reserved characters correctly in the web page , Character entities must be used , The writing format is generally 2 Kind of ：

• &entity_name;

• &#entity_number;

Common character entity ：

• Space ： 

• More than no. ：>

• Less than no. ：<

• &：&

img Elements ： display picture

img The element is specifically used to display picture （img yes image Abbreviation ）

<img src="https://www.baidu.com/img/bd_logo1.png" alt=" The space occupying words are ( When the picture fails to load, it displays )" width="100" height="100">


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src Property is used to set the path of the picture （URL）

• Absolute path ： Full path describing the file location

• Relative paths ： The path relationship with other files caused by the folder where this file is located

  . Represents the current folder , It can be omitted

  .. Represents the parent folder

• For web pages , No matter what operating system , Path separators are /, No \

Be careful ：

• img If the element is only set width, The browser will automatically calculate... According to the image aspect ratio height

  width Empathy

• stay HTML5 Specification ,alt yes img The necessary attributes of the element

• width、height The default unit for is px（ Pixels ）

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) Pictures and pixels

web The commonly used picture formats are ：

• png： static picture , Support transparency

• jpg： static picture , Transparency is not supported

• gif： The dynamic image 、 static picture , Support transparency

Pixels ：

• Pixels （px） Is the smallest unit of image display

• Each pixel can represent a color

• The images displayed by the computer are composed of a pile of pixels

• The more pixels make up the picture , The clearer the display

  

The usual screen resolution , It's usually in pixels ：

a Elements ： Define hyperlinks

a The role of elements ： Define hyperlinks , Used to open a new URL

<!-- Clicking the link will automatically jump to Baidu page -->
<a rel="nofollow" href="https:///www.bbaidu.com"> Baidu </a>


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Common properties

• href： Specify the... To open URL

  Hypertext Reference For short

• target： Where to open URL

target There are the following values

• _self： The default value is , Open... In the current window URL

• _blank： Open in a new window URL

• _parent： Open... In the parent window URL

• _top： Open... In the top window URL

• Some frame Of name value ： In a certain frame Open in URL

  

reflection ：a Element must be used to jump to a new page ？

• Add the following URL Put it in a Elemental href Properties will cause different effects

<!-- Download the file -->
https://github.com/CoderMJLee/MJRefresh/archive/master.zip
<!-- Send E-mail -->
mailto:12345@qq.com
<!-- Open the corresponding tool to download -->
ed2k://|file|%E7%94%9F%E6%B4%BB%E5%A4%A7%E7%88%86%E7%82%B8.The.Big.Bang.Theory.S10E24.END.%E4%B8%AD%E8%8B%B1%E5%AD%97%E5%B9%95.WEB-HR.AAC.1024X576.x264-%E4%BA%BA%E4%BA%BA%E5%BD%B1%E8%A7%86.mp4|194911068|a3285a9ddbea54f5200d3367ec376a58|h=ky54pschiappe5afeqic3oujrue7sxta|/
<!-- Open Xunlei to download -->
thunder://QUFodHRwOi8vNDEuZGwueTgwcy5uZXQ6OTIwLzEzMDMvW+a1t+i0vOeOi13nrKw1ODbpm4YvW+a1t+i0vOeOi13nrKw1ODbpm4ZfaGQubXA0Wlo=


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)iframe Elements ： The embedded HTML file

iframe Elements can implement ： In a HTML Embed other in the document HTML file

<iframe src="https://www.baidu.com" frameborder="1" width="400px" height="400px">
</iframe>


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frameborder Property is used to specify whether a border is displayed ：1- Show 、0- No display

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) Anchor link ： Jump in the web page

Anchor links can achieve ： Jump to a specific location in the web page

<a rel="nofollow" href="#one">go</a>


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Click on go It will be positioned to ：

• id The value is one Any element of

• name The value is one Of a Elements

<a rel="nofollow" href="#"> Back to the top </a>


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If href="#" After clicking, it will Go back to the top of the current page

<a rel="nofollow" href="index.html#one"> The first section of the home page </a>


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Using the above methods can Jump to the specified location on another page

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) Pseudo link ： Click not to jump URL

Pseudo link ： Links that do not specify a specific link address

• Sometimes clicking on a link doesn't want to open a new URL, But want to do something else , You can use Pseudo link

• What do you want to do after clicking the link , The corresponding JavaScript Code

If you don't do anything for the time being , You can write it in the following form ：

<a rel="nofollow" href="#" onclick="return false;"> Pseudo link 1</a>
<a rel="nofollow" href="javascript:"> Pseudo link 2</a>


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So sometimes you can use links as buttons

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) Picture links

img Element heel a Elements used together , Can realize picture link

URL

======================================================================

Browser access  https://www.baidu.com/img/bdlogo.gif The process of ：

What is? URL？

• URL The full name is Uniform Resource Locator（ Uniform resource locator ）

• URL It's the address of the resource 、 Location , Every resource on the Internet has a unique URL

• adopt 1 individual URL, Can find the only one on the Internet 1 A resource

URL The basic format of = protocol://hostname/path = agreement :// The host address / route

URL Common protocols ：

• http： Hypertext transfer protocol , Access to remote network resources , The format is http://

  http Protocol is the most commonly used protocol in network development

  https The agreement is equivalent to http Secure version of the protocol

• file： Access to resources on the local computer , The format is file://（ No need to add the host address ）

• mailto： It's an email address , The format is mailto:

• ftp： Access the file resources of the shared host , The format is ftp://

• ed2k： By supporting ed2k（ Dedicated download link ） Agreed P2P Software access to the resource , The format is ed2k://

  For Software ： Emule

• thunder： By supporting thunder（ Dedicated download link ） Agreed P2P Software access to the resource , The format is thunder://

  For Software ： thunderbolt

URL The more specific and complete syntax format is ：

• protocol://hostname[:port]/path/[;parameters][?query]#fragment

• example ： http://www.baidu.com:80/s?wd=ios#page

port： Port number

• One has IP The host of the address can provide many services , such as Web service 、FTP service 、SMTP Service etc.

• The host by “IP Address + Port number ” To differentiate between different services , The port number is similar to the window of the business hall

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