[Pharo-project] preamble in ChangeSet and ChangeRecord

Hi folks What exactly is the purpose of the preamble in ChangeSet and ChangeRecord? I believe they are not the same for both objects but I haven't been able to figure out what the content of a preamble might actually be. My guess would be that it contains either a comment or a doIt that can check prerequisites. Maybe you could give me an example of how the respective preambles would be used. Thanks, Max