XML in a Nutshell, 3rd Edition

Notations

Since the data in the previous code is not in XML format, the NDATA declaration specifies the type of the data. Here the name jpeg is used. XML does not recognize this as meaning an image in a format defined by the Joint Photographs Experts Group. Rather this is the name of a notation declared elsewhere in the DTD using a NOTATION declaration like this:

<!NOTATION jpeg SYSTEM "image/jpeg">

Here we’ve used the MIME media type image/jpeg as the external identifier for the notation. However, there is absolutely no standard or even a suggestion for exactly what this identifier should be. Individual applications must define their own requirements for the contents and meaning of notations.