Data type

Description

CDATA

Strings can be used in the attribute value.

ID

A unique identifier can be used in the attribute value. If the value is not unique, the XML processor sends an error message.

IDREF

A reference to an identifier that is defined elsewhere in the document can be used in the attribute value. If an identifier that has not been assigned in the current XML document is used as a value, the XML processor sends an error message.

IDREFS

The attribute value may consist of multiple attribute values of the IDREF type that are separated by spaces. If an identifier that has not been assigned in the current XML document is referred to in the attribute value, the XML processor sends an error message.

ENTITY

A reference to a remote binary entity that is declared within the DTD can be used as an attribute value.

ENTITIES

The attribute value may consist of multiple attribute values of the ENTITY type that are separated by spaces.

NMTOKEN

Any combination of letters, numbers, periods, dashes, semi-colons, or underscores may be used as an attribute type.

NMTOKENS

The attribute value may consist of multiple attribute values of the NMTOKEN type that are separated by spaces.

NOTATION

A reference to a notation declared in the DTD can be used as an attribute value.