Thanks Justin - I understand it now.
Creating a script token like {{my.subjectline}} with the content "Hello, this is a subject line" works.
What's not working is this:
Creating a text token {{my.subjectline}} with the content "$subjectline" while defining $subjectline in another script.
Or to be more precise: The latter works on the HTML side of an email, but not on the text side. Also: If you put $subjectline into the Subject Line of an email, it is not displayed on the text side.
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