I've generally found, both with my own code and others' code, that `some-undocumented-special-form' is about as understandable as `some-undocumented-function' (

I've generally found, both with my own code and others' code, that `some-undocumented-special-form' is about as understandable as `some-undocumented-function' (and a similar equivalence for things that are documented).