class

Classes allow CSS and JavaScript to select and access specific elements via the class selectors or functions like the document.getElementsByClassName().

Though the specification doesn't put requirements on the name of classes, web developers are encouraged to use names that describe the semantic purpose of the element, rather than the presentation of the element. For example, attribute to describe an attribute rather than italics, although an element of this class may be presented by italics. Semantic names remain logical even if the presentation of the page changes.

The class attribute is a list of class values separated by ASCII whitespace.

Each class value may contain any Unicode characters (except, of course, ASCII whitespace). However, when used in CSS selectors, either from JavaScript using APIs like Document.querySelector() or in CSS stylesheets, class attribute values must be valid CSS identifiers. This means that if a class attribute value is not a valid CSS identifier (for example, my?class or 1234) then it must be escaped before being used in a selector, either using the CSS.escape() method or manually.

For this reason, it's recommended that developers choose values for class attributes that are valid CSS identifiers that don't require escaping.

• All global attributes.
• element.className
• element.classList
• Introduction to CSS