I'm looking for a way to copy only the headlines and sub-headlines, etc., in
org-mode, without any of the text that had been folded into them. Thus:

/* Bach.

[commentary]

/** Well-Tempered Clavier.

[commentary]

/*** Book I.

[commentary]

/**** Prelude in C Major.

[commentary]

Would become:

/* Bach.
/** Well-Tempered Clavier.
/*** Book I.
/**** Prelude in C Major.

In other words: a way to empty all the headlines in a buffer.