docs: function( selector ){
        var eles = this;
        var fNodes = [];
  
        for( var i = 0; i < eles.length; i++ ){
          var ele = eles[i];
          var eleId = ele.id();
  
          if( !ele.isNode() ){ continue; }
  
          var edges = ele._private.edges;
          for( var j = 0; j < edges.length; j++ ){
            var edge = edges[j];
            var srcId = edge._private.data.source;
            var tgtId = edge._private.data.target;
  
            if( srcId === eleId && tgtId !== eleId ){
              fNodes.push( edge.target()[0] );
            }
          }
        }
  
        return new $$.Collection( this._private.cy, fNodes ).filter( selector );
      }