Use of 'shall', 'should', 'may' and 'can' in Standards?

Standards generally use words, like 'shall', 'should', 'may' and 'can', in mentioning their requirements or guidelines. What these words mean?

Whenever 'shall' is used in a standard, it indicates a requirement that is necessary to follow.

Whenever 'should' is used in a standard, it indicates a recommendation that is recommended to follow the guideline.

Whenever 'may' is used in a standard, it indicates a permission to follow the guideline.

Whenever 'can' is used in the standard, it indicates a possibility or a capability.

With best wishes,

Keshav Ram Singhal