code: function(el, options) {
      // default options for the line
      var defaults = require('../utils/default-options')();
  
      // if we don't pass options, just
      // make it an empty object
      if (typeof options === 'undefined' ) {
          options = {};
      }
  
      options = _.defaults(options, defaults);
      this.width = options.width;
      this.height = options.height;
      this.margin = options.margin;
      
      this.useMarkdown = options.useMarkdown;
  
      this.el = el;
  
      this._data = [];
  
      this.selection = d3.select(el).append('g')
          .attr('class', 'markerSeries');
      if (options.clipId) {
          this.selection.attr('clip-path', 'url(#' + options.clipId + ')');
      }
  
      this.xScale = function() {
          throw new Error('X scale not set');
      };
  
      this.xfield = options.xfield;
      this.xfieldFormat = options.xfieldFormat;
      this.title = options.title;
      this.text = options.text;
      this.type = options.type;
  
      // XXX wire this up
      this.duration = options.duration || 250;
  
      this.currentDatapoint = null;
  
      this.draw_range = null;
  }
docs: event marker constructor