What does define COMMENT_ONLY mean?

[Vladimir Budnev]

Hello!

What does this define

COMMENT_ONLY

mean and what for it is used?

Iv met such one in if_arp.h source in freebsd kernel, but cant get such
strange if in arp header structure.

-----------------------------------example
struct  arphdr {
<...>
/*
 * The remaining fields are variable in size,
 * according to the sizes above.
 */
#ifdef COMMENT_ONLY
        u_char  ar_sha[];       /* sender hardware address */
        u_char  ar_spa[];       /* sender protocol address */
        u_char  ar_tha[];       /* target hardware address */
        u_char  ar_tpa[];       /* target protocol address */
#endif
};