+-------+----+
| Head1 | H2 |
+===+===+====+
| a | b | c  |
+---+---+----+


+-------+----+
| Head1 | H2 |
+===+===+====+ +-------+----+
| a | b | c  | | H1    | H2 |
+---+---+----+ +===+===+====+
               | a | b | c  |
+-------+----+ +---+---+----+
| Head1 | H2 |
+===+===+====+
| a | b | c  |
+---+---+----+