Parsed Versus Unparsed Entities
Earlier, I mentioned that the XML parser will continue parsing the text that is included as the result of reading an entity reference. The only time this is not true is in the case of an external unparsed entity. This special case is the result of including the NDATA keyword with a notation name in a normal general entity declaration such as this:
<!ENTITY flowers_gif SYSTEM "flowers.gif" NDATA gif>
Unparsed entities cannot be referenced within a document using the &entityname; syntax. The only way to refer to unparsed external entities is through the ENTITY attribute type.