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.
(..) - Yeah. Rosita? First part's done. What now? We gotta unwrap the secondary explosives... the dynamite, the RPGs. Make sure these casings are not messed up, and do not mess them up, either. This thing could still blow. (..)2017 TvShow: The Walking Dead Title: Rock in the Road Season: 7 Episode 9