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Should (Requirement)
Should is not per se the specification of a requirement but is used to capture Goals, non-mandatory provisions. Should is used to indicate a goal which must be addressed by the design team but is not formally verified.
Why include should (goal) statements in your requirement document? Because you may have a very important issue that you want to communicate to the developers, but can’t think of a way to do so in the form of a verifiable requirement. For example, NASA was developing a jet pack called SAFER and one of the requirements read “The SAFER shall not impede crew mobility”. Well anything but a decal will probably impeded crew mobility so how am I going to verify that statement if it is written as a requirement? I can’t. So, now that I recognize this, I change the statement from a requirement “shall” to a goal “should” and then I ask my designers and developers at every subsequent review, “how are you going to design the jet pack so that it does not impeded crew mobility”?
Also see: RFC2119 - Key words for use in RFCs to Indicate Requirement Levels
Source: https://reqexperts.com/2012/10/09/using-the-correct-terms-shall-will-should/
