DocBook 4.x formats had to live within the restrictions of being defined by a DTD. The most significant restriction was that an element name uniquely defines its possible contents. That is, an element named codice_19 must contain the same information no matter where it is in the DocBook file. As such, there are many kinds of info elements in DocBook 4.x: codice_26, codice_27, etc. Each has a slightly different content model, but they do share some of their content model. Additionally, they repeat context information. The book's codice_19 element is that, because it is a direct child of the book; it does not need to be named specially for a human reader. However, because the format was defined by a DTD, it did have to be named as such. The root element does not have or need a "version", as the version is built into the DTD declaration at the top of a pre-DocBook 5 document.