docs: function(last) {
  		var me = this;
  		var chart = me.chart;
  		var scale = me._getIndexScale();
  		var stacked = scale.options.stacked;
  		var ilen = last === undefined ? chart.data.datasets.length : last + 1;
  		var stacks = [];
  		var i, meta;
  
  		for (i = 0; i < ilen; ++i) {
  			meta = chart.getDatasetMeta(i);
  			if (meta.bar && chart.isDatasetVisible(i) &&
  				(stacked === false ||
  				(stacked === true && stacks.indexOf(meta.stack) === -1) ||
  				(stacked === undefined && (meta.stack === undefined || stacks.indexOf(meta.stack) === -1)))) {
  				stacks.push(meta.stack);
  			}
  		}
  
  		return stacks;
  	}