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Chapter 6: Classes and IDs
Introduction
Classes and IDs make referencing HTML elements from scripts and stylesheets easier. The class
attribute can be used on one or more tags and is used by CSS for styling. IDs however are
intended to refer to a single element, meaning the same ID should never be used twice. IDs are
generally used with JavaScript and internal document links, and are discouraged in CSS. This
topic contains helpful explanations and examples regarding proper usage of class and ID
attributes in HTML.
Syntax
• class="class1 class2 class3"
• id="uniqueid"
Parameters
Parameter Details
class Indicates the Class of the element (non-unique)
id Indicates the ID of the element (unique in the same context)
Remarks
• Both class and id are global attributes, and may therefore be assigned to any HTML
element.
• Class names must begin with a letter (A-Z or a-z) and can be followed by letters, digits ,
hyphens and underscores.
• In HTML5, the class and id attributes can be used on any element. In HTML 4.0.1, they were
off-limits to the <base>, <head>, <html>, <meta>, <param>, <script>, <style> and <title> tags.
• An element can have one or more classes. Classes are separated by spaces and cannot
contain spaces themselves.
• An element can have only one ID and it must be unique within its context (i.e. a webpage).
IDs also cannot contain spaces themselves.
Examples
Giving an element a class
Classes are identifiers for the elements that they are assigned to. Use the class attribute to assign
a class to an element.
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