In HTML, enumerated attributes are attributes with a limited, predefined set of text values. For example, the global HTML dir attribute has three valid values: ltr , rtl , and auto .

Each enumerated attribute has a default value for when the attribute is present without a value (the value is missing), and a default value for when the attribute is assigned an invalid value. Unlike Boolean HTML attributes — which are always true when the attribute is present whether the value is present, omitted, or invalid — with enumerated HTML attributes, the default for an omitted value may be different from the default for invalid values. For example, the global HTML contenteditable attribute has two valid keywords: true and false . If the attribute is present but no value is set, the value is true . If a value is set, but is invalid, such as contenteditable="contenteditable" , the value maps to a third state, inherit .

ARIA states and properties, being HTML, also have enumerated attributes. If an ARIA attribute includes a both a true and false value in the enumerated list, it generally treats an omitted attribute as false and an invalid value as true , while the default value for the empty string or omitted value depends on the attribute.

For example, the aria-current attribute accepts a limited list of values that includes page , step , location , date , time , true , and false . In this case, if the attribute is not present, is an empty string, is present with no value, or is set to aria-current="false" the attribute is false and is not exposed to the user. Any non-empty string value not in the list of enumerated values is treated as if aria-current="true" were set.

In JavaScript, enumerable properties are those properties whose internal enumerable flag is set to true, which is the default for properties created via simple assignment or via a property initializer. Most iteration mechanisms (such as for...in loops and Object.keys ) only visit enumerable keys.

• Boolean
• JavaScript data types and data structures
• enumerated attributes in the HTML Standard