What does it mean by XLOG_BACKUP_RECORD?

Hi,

While reading source codes I found the following comment in xlog.c.

/*
* Have we passed our safe starting point? Note that minRecoveryPoint is
* known to be incorrectly set if ControlFile->backupEndRequired, until
* the XLOG_BACKUP_RECORD arrives to advise us of the correct
* minRecoveryPoint. All we know prior to that is that we're not
* consistent yet.
*/
if (!reachedConsistency && !ControlFile->backupEndRequired &&
minRecoveryPoint <= lastReplayedEndRecPtr &&
XLogRecPtrIsInvalid(ControlFile->backupStartPoint))

What does XLOG_BACKUP_RECORED means by? I could not find such XLOG info value.
Does it mean XLOG_BACKUP_END?

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center