You're reading the documentation for an older, but still supported version (1.33.4).
For information on the latest version, please have a look at 1.33.5.

OUTPUT_TYPE

This enumeration specifies the output type of the digital outputs installed on the flange, and is defined as follows.

Value	Constant Name	Description
0	OUTPUT_TYPE_PNP	PNP
1	OUTPUT_TYPE_NPN	NPN

Defined in: DRFC.h

typedef enum{
    OUTPUT_TYPE_PNP = 0,
    OUTPUT_TYPE_NPN,
} OUTPUT_TYPE;