Method: Start a new pdf layer.

Method: End the current PDF layer.

Method: Set the visibility of the successive elements.

Method: Add transparency parameters to the current extgstate

Method: Add an extgstate

Method: Put extgstates for object transparency

Method: Set overprint mode for stroking (OP) and non-stroking (op) painting operations.

Method: Get the overprint mode array (OP, op, OPM).

Method: Set alpha for stroking (CA) and non-stroking (ca) operations.

Method: Get the alpha mode array (CA, ca, BM, AIS).