From the forward of the 54 doc.

"It is intended that this voluntary recommended practice will promote and maintain safe working conditions for personnel engaged in well drilling and servicing operations, including special services as they relate to the operation of drilling and well servicing rigs"

Also...

"Recommendations set forth in this publication are viewed as one satisfactory method for accomplishing a desired result. They should not be considered as the only method for achieving the desired results. This publication includes usage of the verbs “shall” and “should,” whichever is deemed most applicable for the specific situation. For the purposes of this publication, the following definitions are applicable:
Shall: Denotes that the recommended practice has universal application to that specific activity.
Should: Denotes a recommended practice: (1) where a safe comparable alternative practice is available; (2) that may be impractical under certain circumstances; or (3) that may be unnecessary for personnel safety under certain circumstances."