2.9.20 BrcMayBeNil
The BrcMayBeNil structure is either a NilBrc or Brc structure, depending on the value of the last four bytes of the structure.
If the last four bytes are 0xFFFFFFFF, the BrcMayBeNil is a NilBrc that specifies that the table cells in question have no border. Otherwise, it is a Brc structure that specifies the border type of table cells.