code: synchronized public int getDTMIdentity(DTM dtm)
    {
  	// Shortcut using DTMDefaultBase's extension hooks
  	// %REVIEW% Should the lookup be part of the basic DTM API?
  	if(dtm instanceof DTMDefaultBase)
  	{
  		DTMDefaultBase dtmdb=(DTMDefaultBase)dtm;
  		if(dtmdb.getManager()==this)
  			return dtmdb.getDTMIDs().elementAt(0);
  		else
  			return -1;
  	}
  				
      int n = m_dtms.length;
  
      for (int i = 0; i < n; i++)
      {
        DTM tdtm = m_dtms[i];
  
        if (tdtm == dtm && m_dtm_offsets[i]==0)
          return i << IDENT_DTM_NODE_BITS;
      }
  
      return -1;
    }
docs: Given a DTM, find the ID number in the DTM tables which addresses
  the start of the document. If overflow addressing is in use, other
  DTM IDs may also be assigned to this DTM.
  
  @param dtm The DTM which (hopefully) contains this node.
  
  @return The DTM ID (as the high bits of a NodeHandle, not as our
  internal index), or -1 if the DTM doesn't belong to this manager.