[racket] Are there any papers that explain Code/Structure Inspectors?

I was playing with #lang racket/gui, and then did,

> (class-info button%)
class-info: current inspector cannot inspect class: #<class:button%>

Reading a bit of the reference manual turned up both "code" and
"structure" inspectors, but I'm not sure how to solve my particular
problem.  That aside, are there any papers that introduce
"inspectors"?

-- 
Ian Tegebo