This word, or the adjective
"RECOMMENDED", mean that there may exist valid reasons in particular
circumstances to ignore a particular item, but the full implications must be
understood and carefully weighed before choosing a different course.
within normative text,
should indicates that among several possibilities one is recommended as
particularly suitable, without mentioning or excluding others, or that a
certain course of action is preferred but not necessarily required. (ISO/IEC)
The CC interprets 'not necessarily required' to mean that the choice of another
possibility requires a justification of why the preferred option was not
chosen. [CC:2006]