#define vs enums?

[raiz]

Hi, does anyone know why #defines are used instead of enums here in 
src/usr.bin/mandoc/man.h?

#define MAN_br   0
#define MAN_TH   1
#define MAN_SH   2
#define MAN_SS   3
#define MAN_TP   4
#define MAN_LP   5
#define MAN_PP   6
#define MAN_P    7
#define MAN_IP   8
#define MAN_HP   9
#define MAN_SM  10
#define MAN_SB  11
#define MAN_BI  12
#define MAN_IB  13
#define MAN_BR  14
#define MAN_RB  15
#define MAN_R   16
#define MAN_B   17
#define MAN_I   18
#define MAN_IR  19
#define MAN_RI  20
#define MAN_sp  21
#define MAN_nf  22
#define MAN_fi  23
#define MAN_RE  24
#define MAN_RS  25
#define MAN_DT  26
#define MAN_UC  27
#define MAN_PD  28
#define MAN_AT  29
#define MAN_in  30
#define MAN_ft  31
#define MAN_OP  32
#define MAN_EX  33
#define MAN_EE  34
#define MAN_UR  35
#define MAN_UE  36
#define MAN_ll  37
#define MAN_MAX 38