My school requires our students to write and reference documents using the Chicago Manual of Style, 7th Ed. Need to settle a debate among professors regarding using a footnote within a footnote. I cannot find any reference to this type of citation. If anyone has ever used a footnote within a footnote, please provide a reference. (For clarification, I am not talking about citing a footnote from another work as in Ambrose, 128n6. I am talking about using a superscript number and commentary inside an existing footnote.) Thanks.

Question

My school requires our students to write and reference documents using the Chicago Manual of Style, 7th Ed.  Need to settle a debate among professors regarding using a footnote within a footnote.  I cannot find any reference to this type of citation.  If anyone has ever used a footnote within a footnote, please provide a reference.  (For clarification, I am not talking about citing a footnote from another work as in Ambrose, 128n6.  I am talking about using a superscript number and commentary inside an existing footnote.) Thanks.