Suggested change:    Allow primary/secondary/tertiary levels

Rationale:   To allow indexing to several levels, and to allow combination of secondary index
                  terms under one main term.


Example:
<INDEXENTRY>
        <LEVEL1><PERSNAME>Shakespeare, William</PERSNAME>
              <LEVEL2><SUBJECT>Plays</SUBJECT>
                <LEVEL3><SUBJECT>Tragedies</SUBJECT></LEVEL3>
                <LEVEL3><SUBJECT>Comedies</SUBJECT></LEVEL3>
              </LEVEL2>
              <LEVEL2><SUBJECT>Letters of, 1600-1605 </SUBJECT>
              </LEVEL2>
        </LEVEL1>
</INDEXENTRY>