code: def selection_index_to_idx(self, key, selection_index):
          '''return a mission idx from a selection_index'''
          a = key.split(' ')
          if a[0] != 'mission' or len(a) != 2:
              print("Bad mission object %s" % key)
              return None
          midx = int(a[1])
          if midx < 0 or midx >= len(self.mission_list):
              print("Bad mission index %s" % key)
              return None
          mlist = self.mission_list[midx]
          if selection_index < 0 or selection_index >= len(mlist):
              print("Bad mission polygon %s" % selection_index)
              return None
          idx = mlist[selection_index]
          return idf selection_index_to_idx(self, key, selection_index):
          '''return a mission idx from a selection_index'''
          a = key.split(' ')
          if a[0] != 'mission' or len(a) != 2:
              print("Bad mission object %s" % key)
              return None
          midx = int(a[1])
          if midx < 0 or midx >= len(self.mission_list):
              print("Bad mission index %s" % key)
              return None
          mlist = self.mission_list[midx]
          if selection_index < 0 or selection_index >= len(mlist):
              print("Bad mission polygon %s" % selection_index)
              return None
          idx = mlist[selection_index]
          return idx
docs: return a mission idx from a selection_index