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.

MESSAGE_INPUT

This structure provides user input information when the robot controller needs to receive and process user input while executing a DRL program. It consists of the following fields.

BYTE#	Field Name	Data Type	Value	Remarks
0	_szText	char[MAX_STRING_SIZE]		256-byte string message information
256	_iType	unsigned char	0~3	Expected input type 0: int, 1: float, 2: string, 3: bool

Total size: 257 bytes

Defined in: DRFS.h

typedef struct _MESSAGE_INPUT
{
    char          _szText[MAX_STRING_SIZE];  /* message string */
    unsigned char _iType;                    /* int:0, float:1, string:2, bool:3 */
} MESSAGE_INPUT, *LPMESSAGE_INPUT;

typedef MESSAGE_INPUT MONITORING_INPUT;