code: function(el, options) {
  
      var defaults = require('../utils/default-options')();
  
      if (typeof options === 'undefined') {
          options = {};
      }
  
      this.options = _.defaults(options, defaults, {
          avoidLabelCollisions : false,
          tickSize : 6,
          tickLabelsVisible : true
      });
  
      this.el = el;
  
      this.selection = d3.select(el);
      this.g = null;
  
      this.axis = d3.svg.axis()
          .orient('bottom')
          .tickSize(0,0)
          .outerTickSize(0);
  
      this.axis.orient('bottom');
  
  }
docs: constructor