Какова цель структуры флагов в iOS?

struct
{
    unsigned resizesCellWidths:1;
    unsigned numColumns:6;
    unsigned separatorStyle:3;
    unsigned allowsSelection:1;
    unsigned backgroundViewExtendsUp:1;
    unsigned backgroundViewExtendsDown:1;
    unsigned usesPagedHorizontalScrolling:1;
    unsigned updating:1;
    unsigned ignoreTouchSelect:1;
    unsigned needsReload:1;
    unsigned allCellsNeedLayout:1;
    unsigned isRotating:1;
    unsigned clipsContentWidthToBounds:1;
    unsigned isAnimatingUpdates:1;
    unsigned requiresSelection:1;
    unsigned contentSizeFillsBounds:1;
    unsigned delegateWillDisplayCell:1;
    unsigned delegateWillSelectItem:1;
    unsigned delegateWillSelectItemMultiTouch:1;
    unsigned delegateWillDeselectItem:1;
    unsigned delegateDidSelectItem:1;
    unsigned delegateDidSelectItemMultiTouch:1;
    unsigned delegateDidDeselectItem:1;
    unsigned delegateGestureRecognizerActivated:1;
    unsigned delegateAdjustGridCellFrame:1;
    unsigned delegateDidEndUpdateAnimation:1;
    unsigned dataSourceGridCellSize:1;
    unsigned int isEditing:1;
    unsigned __RESERVED__:1;
} _flags;

1. Какова цель этой структуры?
2. Что означает нотация : 1 в конце каждой строки?
3. Что означает unsigned модификатор, когда нет явного типа?

Спасибо