code: def is_header(self):
          
          bottom_line = self.text.split('\n')[-1]
  
          if is_only(bottom_line, ['+', '=']):
              return True
  
          return False
docs: Whether or not the cell is a header
  
          Any header cell will have "=" instead of "-" on its border.
  
          For example, this is a header cell::
  
              +-----+
              | foo |
              +=====+
  
          while this cell is not::
  
              +-----+
              | foo |
              +-----+
  
          Returns
          -------
          bool
              Whether or not the cell is a header