code: function checkAppear() {
          if(scroll.delta < opts.delta.speed) {
            if(!deltaSet) {
              deltaSet = true;
              doCheckAppear();
              setTimeout(function(){
                deltaSet = false;
              }, opts.delta.timeout);
            }
          }
          (debounce(function() {
            doCheckAppear();
          }, opts.debounce)());
        }
docs: called on scroll and resize event, so debounce the actual function that does the heavy work of determining if an item is viewable and then "appearing" it