I found this in Jim Reeds's e-mail archives:

      As for tricky pages:  I suppose in the end we just have to make a
      diagram and whereever V text appears (be it a word, a line, or a para),
      define a ``locus'', with locus identifier entered on the diagram,
      and tag the transcribed text with page/locus/line-num.
      Thus, on the page shown on Kahn p865, in addition to the usual
      locus for lines (viz, the main body of text) we could define 8 more
      loci, call them N1, N2, N3, N4, N5, W1, W2, and E1,
      and have lines in the transcription like:

            152 N1 1        OFAN/AFOE       ; ladies with hands in tubing
            152 N2 1        OPOE/ZC89       ; under N1
            152 N3 1        OEFS8OE         ; center top
            152 N4 1        OPOEOR
            152 N5 1        ORSC8AE         ; under N4
            152 W1 1        2ORORAE         ; above lady's head
            152 W2 1        OECOC8N         ; on her vascular boat's hull
            152 E1 1        OFA