The information items discussed so far (document, element, attribute, processing instruction, namespace declaration) all exist outside the realm of physical storage. In general, this is a good thing for most applications that consume XML. However, XML supports composing a single document information item from multiple source files or byte streams for modularity and flexibility. XML makes these underlying units of storage explicit via the notion of entities.[8]

[8] Entities and DTDs are a holdover from the XML's roots in the documentation world. They are presented here largely for completeness. Their functionality is subsumed by XInclude, XBase, and XML Schemas, especially for software-based applications of XML.

Entities are units of ...

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