Hello 
I just thinking out loud… 
Is the header necessary to show by default? I mean it is most of time using the default Summary and probably most of users don’t know that it can be unique and maybe it will be more natural if the text inside details will be truncated with ellipsis and the end will show ...show more if it’s collapsed and show less if expanded. For example the content truncated first line would be the header automatically. This can be a default view but users can add header separately if they want?
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