docs: function(m){
          var x = this.x;
          var y = this.y;
          var z = this.z;
          this.x = x*m[0][0]+y*m[0][1]+z*m[0][2];
          this.y = x*m[1][0]+y*m[1][1]+z*m[1][2];
          this.z = x*m[2][0]+y*m[2][1]+z*m[2][2];
          return this;
      }