The biography uses mostly 'secondary' sources. [=information that did not come from original/primary sources but came from research done by others]
There are some 'secondary' issues/considerations which must be taken into account as well.
In some children's books, the text is 'secondary to' the illustrations.
(..) - This way. Excuse me. Kellerman! Carol, COD says we go to the Pentagon. I have the speaker. Going to the secondary location. Watch yourself. Excuse me, ma'am. Downstairs, second door to the left. Emily. No, no, no, please. Please don't! (..)2013 White House Down