Base Content Type Hierarchy
Windows SharePoint Services 3.0 includes a base hierarchy of site content types. The following figure shows them with their content type IDs. Content types are indented below their parent content types.
As you can see, all content types ultimately inherit from the System content type. This site content type is sealed and cannot be edited. For more information about sealed content types, see Content Type Change Control.
Content types that belong to the "_Hidden" group are not displayed in the user interface for users to apply to lists, or use as the basis for other content types. For more information, see Content Type Access Control.
You can assign content types to list items, documents, and folders. You can assign content types that inherit from the Document site content type only to libraries. Similarly, you can assign content types that inherit from the Item site content type only to lists. Content types that inherit from the Folder content type template can be assigned to either libraries or lists, because both can contain folders.
The content type ID of a content type includes the content type IDs of all the content types from which it inherits, thereby listing its genealogy. For more information, see Content Type IDs.