Every rtObject is a represention of one or several Notes internal rich text components. rtObject contains object specific properties, like width for ruler and column and row count for the table; Color property, Style property and Content property are the most characteristic for most of classes. Some simple objects do not have Content property, i.e. they can not contain other objects; not all object have Color property.
Usually one class deals with functionally separate group of objects, like
rtHotLink deals with URL and other links such as document hotlinks, Notes named element links also
area hotspots, rtSection works with sections, etc.
See the help for specific classes to check the supported properties.