code: def estimate_size(accns, bed, order, conservative=True):
      
      accns = [order[x] for x in accns]
      ii, bb = zip(*accns)
      mini, maxi = min(ii), max(ii)
      if not conservative: # extend one gene
          mini -= 1
          maxi += 1
      minb = bed[mini]
      maxb = bed[maxi]
      assert minb.seqid == maxb.seqid
      distmode = "ss" if conservative else "ee"
      ra = (minb.seqid, minb.start, minb.end, "+")
      rb = (maxb.seqid, maxb.start, maxb.end, "+")
  
      dist, orientation = range_distance(ra, rb, distmode=distmode)
      assert dist != -1
      return dist
docs: Estimate the bp length for the deletion tracks, indicated by the gene accns.
      True different levels of estimates vary on conservativeness.