Unparsed Entities

Unparsed entities are a way to add pointers to your document that point at different kinds of data; the most common application would be for nontextual objects like graphics, video, and other multimedia. To use an unparsed entity, you have to do four things:

1. Declare a notation, which describes the format. Examples would be JPEG, PNG, and VRML.
2. Declare the entity; you have to identify its notation by name and its location by URI.
3. Declare an attribute for some element to be of type ENTITY.
4. Insert one of those elements, provide the attribute, and use the entity as its value.

Here's an example laid out step-by-step:

<!-- 1 -->
<!NOTATION vrml  PUBLIC "VRML 2">
<!-- 2 -->
<!ENTITY Antarctica SYSTEM "http://www.antarctica.net" NDATA vrml>
<!-- 3 -->
<!ATTLIST World src ENTITY #REQUIRED> <!-- 4 -->
<World src='Antarctica'>

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