dc-metadata
dc-metadata provides specific information about the book itself in conformance to the Dublin Core initiative 

Example:

<metadata>
 <dc-metadata xmlns:dc="http://purl.org/metadata/dublin-core/" xmlns:oebpackage="http://openebook.org/namespaces/oeb-package/1.0/ ">
  <dc:Creator role="art">Washington Irving</dc:Creator>
  ...
 </x-metadata>
</metadata>

attributes

id
Provides an element with a unique name within a single document. This is especially useful in works with extensive cross-referencing and linking, such as dictionaries, encyclopedias, or travel guides. Use of ids  simplifies linking and updates.
xml:lang
xml language code.
xmlns:dc
Always equal to "http://purl.org/dc/elements/1.0/"
xmlns:oebpackage
Always equal to "http://openebook.org/namespaces/oeb-package/1.0/"

See also:

<x-metadata>