According to arch-hacker James Gosling, to "...modify a program with no idea whatsoever how it works." (see whacker.) It is actually possible to do this in nontrivial circumstances if the change issmall and well-defined and you are very good at glarking things from context. As a trivial example, it is relatively easy to change all "stderr" writes to "stdout" writes in a piece of C filter code which remains otherwise mysterious. [Jargon File]