A hypertext document, especially a long one, usually covers several aspects of a topic. The elements in a document can be viewed as a concept tree, i.e., the upper element represents a broader concept which covers all the concepts beneath it. Document retrieval can be partially called information retrieval unless the elements expressing appropriate level of concept can be easily retrieved. Thus an effective retrieval system should provide this capability without imposing too much burden on users. To enable it, suitable retrieval techniques, especially advanced indexing techniques need to be developed.