If there is no bibliographic reference, the pair must still be used, they will simply be empty. For a good example of how to encode epigraphs, see James Branch Cabell's The Certain Hour . Identifies a group of lines, such as a stanza or a sonnet. For a good example of how to tag a few stanzas in poetry, see Poe's Annabel Lee . For a good example of how to tag a table, see The 1893 World's Fair .
Many scholarly works contain annotations that require marking.
They must both begin with an alpha character and can contain numbers, a dash, or a period. See Horatio Barber's The Aeroplane Speaks and Enrico Ferri's Criminal Sociology to see two different ways of tagging notes.