Because DITA is an architecture, not just a DTD, you have to ask the question in terms of which infotype (concept, task, reference) , containing which domains. New specializations always increase the count, but the new content models typically have more restricted content models, which limits the selection choices that writers actually see in a validating XML editor.

The following count is based on the developerWorks-based dita13 toolkit, which predates the OASIS DITA 1.0 Standard.

The unspecialized topic dtd in DITA has 94 elements.

The 4 basic domains (software, programming, highlighting, UI) contribute 49 elements, which brings the count for domain-specialized topic dtd to 143 elements. Since these domains are also added to each of the dtds derived from topic, this is the base count affecting the rest of the per-dtd totals.

Concept.dtd adds 2 elements for its single-dtd total of 145 elements.

Task.dtd adds 25 elements for its single-dtd total of 168 elements.

Reference.dtd add 12 elements for its single-dtd total of 155 elements.

Ditabase.dtd adds 1 element but includes the sum of new elements in all the infotypes, having a grand total of 183 elements.