Andrew Ayer's The Difference Between Root Certificate Authorities, Intermediates, and Resellers is about exactly that issue in much more detail than what I wrote recently . Although I knew some of the information in this article, other pieces were new to me.

Also very relevant to this area is Ayer's earlier The SSL Certificate Issuer Field is a Lie . This covers what it says in the title and is a fun read; the rabbit hole goes pretty deep.