HTML Introduction
What is HTML?
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HTML stands for Hyper Text Markup Language超文本标记语言
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HTML is the standard markup language for creating Web pages
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HTML describes the structure of a Web page
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HTML consists of a series of elements
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HTML elements tell the browser how to display the content
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HTML elements label pieces of content such as "this is a heading", "this is a paragraph", "this is a link", etc.
What is an HTML Element?
An HTML element is defined by a start tag, some content, and an end tag:
The HTML element is everything from the start tag to the end tag:
Web Browsers
The purpose of a web browser (Chrome, Edge, Firefox, Safari) is to read HTML documents and display them correctly.
A browser does not display the HTML tags, but uses them to determine how to display the document:
HTML Documents
All HTML documents must start with a document type declaration: <!DOCTYPE html>.
The HTML document itself begins with <html> and ends with </html>.
The visible part of the HTML document is between <body> and </body>.
The <!DOCTYPE> Declaration
The <!DOCTYPE> declaration represents the document type, and helps browsers to display web pages correctly.
It must only appear once, at the top of the page (before any HTML tags).
The <!DOCTYPE> declaration is not case sensitive.
HTML Headings
HTML headings are defined with the <h1> to <h6> tags.
<h1> defines the most important heading. <h6> defines the least important heading:
HTML Paragraphs
HTML paragraphs are defined with the <p> tag
HTML Links
HTML links are defined with the <a> tag
The link's destination is specified in the href attribute.
Attributes are used to provide additional information about HTML elements.
HTML Attributes
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All HTML elements can have attributes
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Attributes provide additional information about elements
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Attributes are always specified in the start tag
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Attributes usually come in name/value pairs like: name="value"
The href Attribute
The <a> tag defines a hyperlink. The href attribute specifies the URL of the page the link goes to:
The src Attribute
The <img> tag is used to embed an image in an HTML page. The src attribute specifies the path to the image to be displayed:
There are two ways to specify the URL in the src attribute:
1. Absolute URL - Links to an external image that is hosted on another website. Notes: External images might be under copyright. If you do not get permission to use it, you may be in violation of copyright laws. In addition, you cannot control external images; it can suddenly be removed or changed.
2. Relative URL - Links to an image that is hosted within the website. Here, the URL does not include the domain name. If the URL begins without a slash, it will be relative to the current page. Example: src="img_girl.jpg". If the URL begins with a slash, it will be relative to the domain. Example: src="/images/img_girl.jpg".
Tip: It is almost always best to use relative URLs. They will not break if you change domain.
The width and height Attributes
The <img> tag should also contain the width and height attributes, which specifies the width and height of the image (in pixels像素):
The alt Attribute
The required alt attribute for the <img> tag specifies an alternate text for an image, if the image for some reason cannot be displayed. This can be due to slow connection, or an error in the src attribute, or if the user uses a screen reader.
HTML Headings
HTML headings are defined with the <h1> to <h6> tags.
<h1> defines the most important heading. <h6> defines the least important heading.
HTML Paragraphs
The HTML <p> element defines a paragraph.
A paragraph always starts on a new line, and browsers automatically add some white space (a margin边缘) before and after a paragraph.
HTML Styles
Setting the style of an HTML element, can be done with the style attribute.
The HTML style attribute has the following syntax:
<tagname style="property:value;">
The property is a CSS property. The value is a CSS value.
The CSS background-color property defines the background color for an HTML element.
The CSS color property defines the text color for an HTML element:
The CSS font-family property defines the font to be used for an HTML element:
The CSS font-size property defines the text size for an HTML element:
The CSS text-align property defines the horizontal text alignment for an HTML element
HTML Text Formatting Elements Tag Description <b> Defines bold text <em> Defines emphasized text <i> Defines a part of text in an alternate voice or mood <small> Defines smaller text <strong> Defines important text <sub> Defines subscripted text <sup> Defines superscripted text <ins> Defines inserted text <del> Defines deleted text <mark> Defines marked/highlighted text
HTML Comments
You can add comments to your HTML source by using the following syntax:
<!-- Write your comments here -->
Notice that there is an exclamation point (!) in the start tag, but not in the end tag.