docs: function passthru_prelude(tokenOrForm) {
    // the expression returned is a "no-op" represented as (nop)
    // it's only purpose is to have something for the prelude to hang on
    // (note we scrub "(nop)" from the pretty-printed parse trees btw)
    var nop = sl.list("nop");
    if(tokenOrForm && tokenOrForm.prelude) {
      nop.prelude = tokenOrForm.prelude;
    }
    return nop;
  }