code: function Line( graph ) {
  
  	// INSTANCE ATTRIBUTES //
  
  	this._parent = graph;
  	this._root = undefined;
  	this._children = {};
  	this._config = {
  		"type": "line",
  		"interpolation": {
  			"mode": "linear",
  			"tension": 0.7
  		},
  		"labels": []
  	};
  
  	// DATA //
  
  	this._data = graph._data;
  
  	// TRANSFORMS //
  
  	this._transforms = {
  		'x': function X( d ) {
  			return graph._xScale( d[ 0 ] );
  		},
  		'y': function Y( d ) {
  			return graph._yScale( d[ 1 ] );
  		}
  	};
  
  	// GENERATOR //
  
  	this._path = this.path()
  		.x( this._transforms.x )
  		.y( this._transforms.y )
  		.interpolate( this._config.interpolation.mode )
  		.tension( this._config.interpolation.tension );
  
  	// REGISTER //
  	if ( graph._config.hasOwnProperty( 'marks' ) ) {
  		graph._config.marks.push( this._config );
  	} else {
  		graph._config.marks = [ this._config ];
  	}
  	if ( graph._children.hasOwnProperty( 'marks' ) ) {
  		graph._children.marks.push( this );
  	} else {
  		graph._children.marks = [ this ];
  	}
  
  	return this;
  }
docs: Line // 
  FUNCTION: Line( graph )
  Line constructor. Creates a new line instance.
  
  @constructor
  @param {object} graph - parent graph instance
  @returns {object} line instance