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HTML attribute reference

Elements in HTML have attributes; these are additional values that configure the elements or adjust their behavior in various ways to meet the criteria the users want.

Attribute list

Attribute Name	Elements	Description
accept	,	List of types the server accepts, typically a file type.
accept-charset		List of supported charsets.
accesskey	Global attribute	Keyboard shortcut to activate or add focus to the element.
action		The URI of a program that processes the information submitted via the form.
align Deprecated	, , , , , , , , , , , ,	Specifies the horizontal alignment of the element.
allow		Specifies a feature-policy for the iframe.
alt	, ,	Alternative text in case an image can’t be displayed.
async		Executes the script asynchronously.
autocapitalize	Global attribute	Sets whether input is automatically capitalized when entered by user
autocomplete	, , ,	Indicates whether controls in this form can by default have their values automatically completed by the browser.
autoplay	,	The audio or video should play as soon as possible.
background	, , ,	Specifies the URL of an image file.

Note: Although browsers and email clients may still support this attribute, it is obsolete. Use CSS background-image instead.

Background color of the element.

Note: This is a legacy attribute. Please use the CSS background-color property instead.

Note: This is a legacy attribute. Please use the CSS border property instead.

This attribute sets the text color using either a named color or a color specified in the hexadecimal #RRGGBB format.

Note: This is a legacy attribute. Please use the CSS color property instead.

Specifies the height of elements listed here. For all other elements, use the CSS height property.

Note: In some instances, such as , this is a legacy attribute, in which case the CSS height property should be used instead.

Specifies a Subresource Integrity value that allows browsers to verify what they fetch.

Note: This attribute is obsolete, use instead.

For the elements listed here, this establishes the element’s width.

Note: For all other instances, such as , this is a legacy attribute, in which case the CSS width property should be used instead.

Content versus IDL attributes

In HTML, most attributes have two faces: the content attribute and the IDL (Interface Definition Language) attribute.

The content attribute is the attribute as you set it from the content (the HTML code) and you can set it or get it via element.setAttribute() or element.getAttribute() . The content attribute is always a string even when the expected value should be an integer. For example, to set an element’s maxlength to 42 using the content attribute, you have to call setAttribute(«maxlength», «42») on that element.

The IDL attribute is also known as a JavaScript property. These are the attributes you can read or set using JavaScript properties like element.foo . The IDL attribute is always going to use (but might transform) the underlying content attribute to return a value when you get it and is going to save something in the content attribute when you set it. In other words, the IDL attributes, in essence, reflect the content attributes.

IDL attributes are not always strings; for example, input.maxlength is a number (a signed long). When using IDL attributes, you read or set values of the desired type, so input.maxlength is always going to return a number and when you set input.maxlength , it wants a number. If you pass another type, it is automatically converted to a number as specified by the standard JavaScript rules for type conversion.

IDL attributes can reflect other types such as unsigned long, URLs, booleans, etc. Unfortunately, there are no clear rules and the way IDL attributes behave in conjunction with their corresponding content attributes depends on the attribute. Most of the time, it will follow the rules laid out in the specification, but sometimes it doesn’t. HTML specifications try to make this as developer-friendly as possible, but for various reasons (mostly historical), some attributes behave oddly ( select.size , for example) and you should read the specifications to understand how exactly they behave.

Boolean Attributes

Some content attributes (e.g. required , readonly , disabled ) are called boolean attributes. If a boolean attribute is present, its value is true, and if it’s absent, its value is false.

HTML defines restrictions on the allowed values of boolean attributes: If the attribute is present, its value must either be the empty string (equivalently, the attribute may have an unassigned value), or a value that is an ASCII case-insensitive match for the attribute’s canonical name, with no leading or trailing whitespace. The following examples are valid ways to mark up a boolean attribute:

div itemscope>This is valid HTML but invalid XML.div> div itemscope=itemscope>This is also valid HTML but invalid XML.div> div itemscope="">This is valid HTML and also valid XML.div> div itemscope="itemscope"> This is also valid HTML and XML, but perhaps a bit verbose. div> 

To be clear, the values » true » and » false » are not allowed on boolean attributes. To represent a false value, the attribute has to be omitted altogether. This restriction clears up some common misunderstandings: With checked=»false» for example, the element’s checked attribute would be interpreted as true because the attribute is present.

Event handler attributes

Warning: The use of event handler content attributes is discouraged. The mix of HTML and JavaScript often produces unmaintainable code, and the execution of event handler attributes may also be blocked by content security policies.

In addition to the attributes listed in the table above, global event handlers — such as onclick — can also be specified as content attributes on all elements.

All event handler attributes accept a string. The string will be used to synthesize a JavaScript function like function name(/*args*/) , where name is the attribute’s name, and body is the attribute’s value. The handler receives the same parameters as its JavaScript event handler counterpart — most handlers receive only one event parameter, while onerror receives five: event , source , lineno , colno , error . This means you can, in general, use the event variable within the attribute.

div onclick="console.log(event)">Click me!div> div onclick="console.log(onclick)">Click me!div> 

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Tags, Attributes, and Elements

Although the basics of HTML is plain text, we need a bit more to make it a nice and shiny HTML document.

Tags

The basic structure of an HTML document includes tags, which surround content and apply meaning to it.

Change your document so that it looks like this:

    This is my first web page  

Now save the document again, go back to the web browser and reload the page.

The appearance of the page will not have changed at all, but the purpose of HTML is to apply meaning, not presentation, and this example has now defined some fundamental elements of a web page.

The first line on the top, , is a document type declaration and it lets the browser know which flavor of HTML you’re using (HTML5, in this case). It’s very important to stick this in — If you don’t, browsers will assume you don’t really know what you’re doing and act in a very peculiar way.

To get back to the point, is the opening tag that kicks things off and tells the browser that everything between that and the closing tag is an HTML document. The stuff between and is the main content of the document that will appear in the browser window.

Closing tags

The and put a close to their respective elements (more on elements in a moment).

Not all tags have closing tags like this ( ) some tags, which do not wrap around content will close themselves. The line-break tag for example, looks like this :
— a line break doesn’t hold any content so the tag merrily sits by its lonely self. We will come across these examples later. All you need to remember is that all tags with content between them should be closed, in the format of opening tag → content → closing tag. It isn’t, strictly speaking, always a requirement, but it’s a convention we’re using in these tutorials because it’s good practice that results in cleaner, easier to understand code.

You might come across “self-closing” tags, whereby a br tag, for example, will look like “
” instead of simply “
”. This is a remnant of XHTML, a form of HTML based on another markup language called XML. HTML5 is much more chilled out than XHTML and will be happy with either format. Some developers prefer one way, some prefer the other. We tossed a coin and decided to stick with the simpler version.

Attributes

Tags can also have attributes, which are extra bits of information. Attributes appear inside the opening tag and their values sit inside quotation marks. They look something like Margarine . We will come across tags with attributes later.

Once again, quotation marks aren’t always essential but it is a good-practice convention HTML Dog uses for consistency and clarity. We suggest you do the same.

Elements

Tags tend not to do much more than mark the beginning and end of an element. Elements are the bits that make up web pages. You would say, for example, that everything that is in between (and includes) the and tags is the body element. As another example, whereas “ ” are tags, “ ” is a title element.

Related pages

References

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