Document

The document container serves as a root container for regular web pages, and as boundary to separate document content from other UI elements in web applications.

Example 1: for all your web pages you want to configure a default font, so you configure the document-font-family design token.

Example 2: in a text editor you might have a layout with a toolbar, sidebar and a document. In the document you can open a context menu. The application container would be applied to the root, and on the context menu.