There are several modules that provide the basic topic elements and attributes. Some are specific to topic and its specializations, others are shared with DITA maps.

tblDecl.mod (DTD)

tblDeclMod.xsd, tblDeclGrp.xsd (Schema)

Defines the elements for authoring tables, based on the CALS table model but with some DITA-specific extensions.

metaDecl.mod (DTD)

metaDeclMod.xsd, metaDeclGrp.xsd (Schema)

Defines metadata elements, which can appear in both topics and in maps, where metadata can be defined for multiple topics at once.

commonElements.mod, commonElements.ent (DTD

commonElementsGrp.xsd (Schema)

Defines common elements such as ph or keyword that appear in both topics and maps.

topicAttr.mod, topicDefn.ent (DTD only - folded into other schema files))

Common DITA attributes and entities.

xml.xsd, ditaarch.xsd (Schema only - folded into other DTD files)

Common XML attributes and the DITA architecture version attribute

topic.mod (DTD)

topicMod.xsd, topicGrp.xsd (Schema)

Defines the rest of the elements in a topic.