## 29.4 Document Type Definitions (cont.)

- Expressions to describe children:

  Rule Description | Element Content
  --- | ---
  `EMPTY` | No children allowed
  (E*) | Any sequence of 0 or more elements E
  (E+) | Any sequence of 1 or more elements E
  (E?) | Optional element E (0 or 1)
  (E1, E2, . . .) | Element E1, followed by E2, ...
  (E1|E2|. . .) | Element E1 or E2 or ...
  (`#PCDATA`) | Text only (parsable)
  (`#PCDATA`|E1|E2|. . .)* | Any sequence of text and elements E1, E2, ..., in any order
  `ANY` | Any children allowed

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