DITA 1.3 is compatible with prior versions of the DITA specification; all valid DITA
1.0, 1.1, and 1.2 documents are valid DITA 1.3 documents. However, some changes to existing
document-type shells and specializations might be needed in order to maintain the same behavior
under DITA 1.3 or to take full advantage of new DITA 1.3 features.