However, the object at the other end of the link does not necessarily encode the reverse path in its usual visual representation. All links must be bidirectional. Folders have names. Folders are sometimes arranged in a hierarchy. Each such message is a message in its own right, but the containment relationship can be important.
Messages have bodies.
The bodies can contain unstructured text. The bodies can contain text that is named , for example, an attached text file which has a file name or description specified in its attachment headers. The bodies can contain binary objects which, while not textually searchable, are named and described. Bodies can contain hyperlinks. Plain-text messages might happen to have detectable URLs in them, and HTML messages have many mechanisms for referring to other objects.