code: function() {
        var activeFaces = [];
  
        for (var i = 0; i < this.faces.length; i++) {
          var face = this.faces[i];
  
          if (face.mark === Visible) {
            activeFaces.push(face);
          }
        }
  
        this.faces = activeFaces;
  
        return this;
      }
docs: Removes inactive faces