A DTD defines the structure and the legal elements and attributes of an XML document. In particular, the XML eCTD DTD (Document Type Definition) defines the overall structure of the submission. The purpose of the XML backbone is two-fold: (1) to manage meta-data for the entire submission and each document within the submission and (2) to constitute a comprehensive table of contents and provide corresponding navigation aids. Meta-data on submission level include information about submitting and receiving organization, manufacturer, publisher, ID and kind of the submission, and related data items. Examples for meta-data on document level are versioning information, language, descriptive information such as document names and checksums.