An entity is a unit of content that can be placed in content using an entity reference. All entities are nodes, where the node-name attribute contains the name of the entity. The children of the node represents the content of the entity.
public-id entity
The public-id attribute provides the public identifier of the entity, or NIL if left unspecified.
system-id entity
The system-id attribute provides the system identifier of the entity, or NIL if left unspecified.
notation-name entity
The notation-name attribute provides the name of the notation for the entity.