gitconnected, a Medium site, posted “How A Simple 500-Word Memo Changed the Way We Talk About the Internet”, discussing RFC-2119, “Key words for use in RFCs to Indicate Requirement Levels”, which addresses the specific meaning of weasel words in formal specifications.

The actual RFC itself is pretty short, but it covers the exact meaning of the words and phrases “must”, “must not”, “should”, “should not”, and “may.” Excellent guidance for people writing (or working with) specifications, because it indicates what a specification absolutely requires versus what it may require (see?) and also demands guidance for when things might not comply.