code: function startYielding(ms) {
          API.stopYielding();
          ms = ms || 1000;
          var yielding = setInterval(function () {
            yieldclbcks.forEach(function (clbck) { clbck(); });
          }, ms);
          API.stopYielding = function() { clearInterval(yielding); };
          return this;
        }
docs: Start the periodic yielding (every ms)