"Shall" and "shall not" identify requirements to be followed strictly to conform to this document and from which no deviation is permitted.
"Should" and "should not" indicate that one of several possibilities is recommended as particularly suitable, without mentioning or excluding others, that a certain course of action is preferred but not necessarily required, or that (in the negative form) a certain possibility or course of action is discouraged but not prohibited.
"May" and "need not" indicate a course of action permissible within the limits of the document.
"Can" and "cannot" are used for statements of possibility and capability, whether material, physical or causal.
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