docs: function buttonsFromAllFeatures() {
        const buttons = $scope.features.buttons.map( ( button, i ) => {
           button.fallbackIndex = i + DEFAULT_BUTTONS.length;
           return button;
        } );
        DEFAULT_BUTTONS.forEach( ( buttonFeatureName, i ) => {
           const button = $scope.features[ buttonFeatureName ];
           if( button ) {
              button.fallbackIndex = i;
              buttons.push( button );
           }
        } );
        return buttons.filter( button => button.enabled );
     }