code: def process_anchor_start(regions_fn, to_count_fn,
                           anchor_to=ANCHOR_START, normalize=False,
                           verbose=False):
    
    res = []
    possible = []
    trees = intervalTrees(to_count_fn, verbose=verbose)
    for region in BEDIterator(regions_fn, verbose=verbose):
      if normalize:
        for i in range(0, len(region)):
          while len(possible) <= i:
            possible.append(0)
          possible[i] += 1
  
      if region.chrom not in trees:
        continue
      hits = trees[region.chrom].intersectingInterval(region.start, region.end)
      for h in hits:
        abs_pos = h.start
        if abs_pos < region.start or abs_pos >= region.end:
          continue
        rel_pos = __to_relative(abs_pos, region, anchor_to)
        assert(rel_pos < len(region))
  
        while(len(res) <= rel_pos):
          res.append(0)
        res[rel_pos] += 1
  
    if normalize:
      __norm_counts(res, possible)
    return res
docs: :return: list where each element is the number of hits at that location
             relative to the start of the regions.