The processor is not expected to rearrange, select, or suppress any of the elements, but simply present them as specified. A set of declarations that defines the names of the elements and their attributes, and that specifies rules for their combination or sequence. Most elements have start and end tags and contain some part of the document content.
Empty elements have only a start tag and have no content.
An exclusion is used in a DTD to indicate that, within the element on which the exclusion occurs, the excluded elements are not valid anywhere within the content of the element. For example, in DocBook, Footnote excludes Footnote . This means that footnotes cannot nest, even though Footnote contains Para , and Footnote occurs in the proper content model of Para . See Section 1.4.2.1 . An external entity is a general entity that refers to another document.