The writing style of a requirement is also important. Although there is some variation in standards between organizations, a general guideline is that all requirements describing a mandatory system property use the words ‘shall’ or ‘must.’ Words such as “will” are generally reserved to depict events that will happen in the future and are not used to describe properties of the system. Certainly words such as “ought to”, “should”, “would”, “might”, and “may” do not belong in a requirement because they immediately introduce the idea of an optional feature and therefore do not result in contractually binding requirements.