In Xport, the term root document is used to refer to a document which includes the html, head, title, and body elements. If an xhtml document, or document object, does not include all three of these root elements, it is not considered a root document. Root documents are normally created by including the argument root_doc in the constructor of the document, like below.

document myStrictDoc(root_doc);
tdocument myTransitionalDoc(root_doc);
    

By supplying the root_doc argument, you're specifying that the document object will be created with the html, head, and body elements included. If this argument is not supplied, the document will be empty, and will not include any elements.