Entities are symbolic names that are used to insert text into a file. The text that an entity refers to can be a simple string of characters or it can be the text from an entire file.

An entity reference is used to insert the text associated with the entity. Entities must be declared in the declaration subset of the DOCTYPE declaration before they can be referred to. To refer to the entity in the source file, the entity name is preceded by an ampersand (&) to indicate it is an entity or percent (%) to indicate it is a parameter entity. Both types of entities are ended with a semicolon (;). A blank or the end of the line can be used to end the entity reference instead of the semicolon.

Because entity declarations can only be made within the declaration subset, the parameter entity is the only way to embed a file of entity declarations. Parameter entities are used when an entity reference is needed in the declaration subset. References to parameter entities can only be made in the declaration subset.

Because entity names are case-sensitive, ensure that references to entities are specified correctly.