Function extract_essence 

pub fn extract_essence<'i>(
    lines: impl IntoIterator<Item = &'i HeaderValue>,
) -> Option<Cow<'i, str>>

Available on crate features http and std only.

The type/subtype of the extracted type, as sent: all a decision on the media type needs.

Borrowed from the lines, unless a quoted string one line leaves open runs into the next.