It is an acronym commonly used by professional lexicographs: the DTD, i.e. the Document Type Description. In other words, almost all new electronic dictionaries, be they paper-based dictionaries for computerisation or dictionaries designed directly for electronic media, actually go through an essential phase: the development of the DTD. At the request of Jean Pruvost, I tried here to clarify what this is about, by giving an illustration and trying to get the fundamental aspects properly understood, whether it is the quality search established between the producer, the designer and the reader of the document, or whether it is the precise set of tags to be installed to code each type of information in a uniform manner. The verification and programmable evolution of the DTD of a given dictionary should also be borne in mind. In fact, a good DTD depends on the quality of the multiple and transversal queries that the computer reader can then launch in the dictionary.