Two distinct DITA document types that are taken from different tools or environments might be functionally equivalent.
A DITA document type is defined by the following:
- The set of modules that are declared in the domains attribute on the root element of the document
- The values of the class attributes of all the elements in the document
- Rules for topic nesting
Two document-type shells define the same DITA document type if they integrate identical vocabulary modules, constraint modules, and rules for topic nesting. For example, a document type shell that is an unmodified copy of the OASIS-provided document-type shell for topic defines the same DITA document type as the original document-type shell. However, the new document-type shell has the following differences:
- It is a distinct file that is stored in a different location.
- It has a distinct system identifier.
- If it has a public identifier, the public identifier is unique.