David, Toby,
yes and right. it is no tapping but more a touch and let go.
The name typewriter says it very well. Touch the strings lightly as if you press down a typewriter and mmediately after hitting the string release it again. It is a bit like doing slapping with your thumb but only with your fingertips. You can use it with one finger or with all four fingers at the end of the fingerboard. But also John used this with a normal fingerstyle playing. If you look closely at his playing you will notice that also then he has the tapewriter motion than the normal plugging of the string. This combined with the low action you really get fast and get that strong overtones. Due to this you have to develop a light touch and that is also what John did. There was no power in his playing, it was the gentle and most controlled touch. And David, you are right: of course a strongt left hand pressure/muting combined with many open string playing. Look closely at his playing. You will see that he buildt up walks and licks combined with fretted and open strings, constantly.
Sorry guys, it is really hard to explain without showing.
Any questions, plse ask.
Oliver (Spyderman)