Function header 

pub fn header<'a>(
    columns: &[Column<'a>],
    style: &TableStyle,
    cutoff: Priority,
) -> Row<'a>

The heading row for the columns kept at cutoff.

Exposed beside table because a caller assembling its own Table still has to draw a header that agrees with the body about what just disappeared. Assembling it a second time by hand is how they stop agreeing.