[NortySpock]

Sometimes I've tried to leave comments and notes if I detect a good place for a seam (to use Michael Feather's term), usually around an encapsulating function where I say something like:

    // TODO: This is the simple version that assumes [our current assumption]    
    //If you need to handle multiple cases here, I suggest [X strategy].
    void doThing()
    {
      //existing code 
    }