No mystery
eg Runway Stabilizer < >
Boeings explanation is in the FCOM:
Special Note < XXX >
This FCOM contains information which has been included at the request of XXX. for airplanes covered by this manual. This information may differ
from Boeing recommended information. By including this information in the
manual, Boeing is providing a publishing service only and such inclusion does not imply that The Boeing Company in any way endorses or approves such
information. The technical accuracy and validity of all such airline provided
information, and its effect, if any, on other portions of this manual, is the sole
responsibility of XXX.