Definition and Usage
This element tells a browser that this is an HTML document.
Differences Between HTML and XHTML
The xmlns attribute is required in XHTML but not in HTML. However, the validator on w3.org does not complain when this attribute is missing from the <html> tag in an XHTML document. This is because "xmlns=http://www.w3.org/1999/xhtml" is a fixed value and will be added to the <html> tag even if you do not include it. 数据挖掘实验室
Example
| <html xmlns="http://www.w3.org/1999/xhtml">
<head> <body> </html> |
Required Attributes
DTD indicates in which DTD the attribute is allowed. S=Strict, T=Transitional, and F=Frameset. 数据挖掘研究院
| Attribute | Value | Description | DTD |
|---|---|---|---|
| xmlns | http://www.w3.org/1999/xhtml | Defines the XML namespace attribute | STF |
Standard Attributes
| dir, lang, xml:lang |
HTML tags can have attributes. The special attributes for each tag are listed under each tag description. The attributes listed here are the core and language attributes that are standard for all tags (with a few exceptions).
Core Attributes
Not valid in base, head, html, meta, param, script, style, and title elements. 数据挖掘研究院
| Attribute | Value | Description |
|---|---|---|
| class | class_rule or style_rule | The class of the element |
| id | id_name | A unique id for the element |
| style | style_definition | An inline style definition |
| title | tooltip_text | A text to display in a tool tip |
Language Attributes
Not valid in base, br, frame, frameset, hr, iframe, param, and script elements.
| Attribute | Value | Description |
|---|---|---|
| dir | ltr | rtl | Sets the text direction |
| lang | language_code | Sets the language code |
Keyboard Attributes
| Attribute | Value | Description |
|---|---|---|
| accesskey | character | Sets a keyboard shortcut to access an element |
| tabindex | number | Sets the tab order of an element |
