code: def _unique_name(name, seen):
          
          if name in seen:
              n = seen[name]
              while (name + ".%d" % n) in seen:
                  n += 1
              seen[name] = n + 1
              name += ".%d" % n
          seen[name] = 1
          return name
docs: Append incremental '.N' suffix if glyph is a duplicate.