Why is _POSIX_SOURCE used instead of __BSD_VISIBLE in <termios.h>?

[Sebastian Huber]

Hello,

the Termios header <termios.h>, <sys/_termios.h>, etc. use sometimes 
_POSIX_SOURCE directly to determine if a thing should be exposed to the 
user, e.g.

#ifndef _POSIX_SOURCE
#define    ONLCR        0x00000002    /* map NL to CR-NL (ala CRMOD) */
#define    TABDLY        0x00000004    /* tab delay mask */
#define        TAB0        0x00000000        /* no tab delay and 
expansion */
#define        TAB3        0x00000004        /* expand tabs to spaces */
#define    ONOEOT        0x00000008    /* discard EOT's (^D) on output) */
#define    OCRNL        0x00000010    /* map CR to NL on output */
#define    ONOCR        0x00000020    /* no CR output at column 0 */
#define    ONLRET        0x00000040    /* NL performs CR function */
#endif  /*_POSIX_SOURCE */

This circumvents the feature mechanisms of <sys/cdefs.h>. Why is 
__BSD_VISIBLE not used for this?

-- 
Sebastian Huber, embedded brains GmbH

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