patch(1) outputs ed(1) commands. It always worked that way, and it demonstrates the power of the "do one thing and do it well": patch just does the analysis and

patch(1) outputs ed(1) commands. It always worked that way, and it demonstrates the power of the "do one thing and do it well": patch just does the analysis and generates the appropriate editting commands, but the editting is passed on to a program specialized for just that: ed(1). It as also a good showcase for UNIX modularity principle.