Unparsed entities are used in attribute values and are referenced by name. If the name of an unparsed entity appears in an attribute value declared as being of type ENTITY or ENTITIES, a validating XML processor must pass both the system identifier and the public identifier for the unparsed entity to the application.
The content of an unparsed entity may be text or other types of data. If it is text, then it can be XML or some other format.
An unparsed entity is declared using the following format:
<!ENTITY entityName SYSTEM "myPicture.gif" NDATA gif>
The entityName is used in attribute values to reference the unparsed entity. The filename of the entity is given in quotation marks following the SYSTEM keyword. The keyword ...