making | include the headers

[jidanni]

Nowadays | doesn't include the headers.

We read:
The properties `:decode' and `:headers' that are put to the function
symbol `gnus-summary-save-in-pipe' control whether this function
decodes articles and what headers to keep (see the doc string for the
`gnus-default-article-saver' variable).

OK, I did read that. But I still don't understand what I need to setq in
.gnus.el to make | always include the headers.