It seems to me that in English usage "set off" is almost irreplaceable in the collocation I refer to in the question and in similar phrases, e.g., "comma(s) set(s) off (this or that)." As if everyone is afraid to use a synonym or a synonymous phrase – almost like a conspiracy. To me it sounds like a person who is parroting the same words over and over again without 100% understanding of what the words mean.
Please, can somebody provide a definitive definition of "set off" in the above-mentioned context?
PS Perhaps I just need access to a really good big dictionary, but, unfortunately, I ain't got one. In the following link, for example, "set off" and "separate" are treated as two distinct concepts, but it doesn't help me to understand what the words "set off" mean: http://www.cws.illinois.edu/workshop/writers/tips/commas/
PPS Please correct my writing if I've made any mistakes. Thank you.