——为特定类型的子元素提供现成的查询的类所采用的协议
——这些属性表示暴露于可访问系统中的数据，并在查询匹配过程中可用。
———————————————————————————————————————
Descendant Element Queries
//常用的
@property(readonly, copy) XCUIElementQuery *activityIndicators;
@property(readonly, copy) XCUIElementQuery *alerts;
@property(readonly, copy) XCUIElementQuery *buttons;
@property(readonly, copy) XCUIElementQuery *cells;
@property(readonly, copy) XCUIElementQuery *collectionViews;
@property(readonly, copy) XCUIElementQuery *datePickers;
@property(readonly, copy) XCUIElementQuery *groups;
@property(readonly, copy) XCUIElementQuery *icons;
@property(readonly, copy) XCUIElementQuery *images;
@property(readonly, copy) XCUIElementQuery *keyboards;
@property(readonly, copy) XCUIElementQuery *pickers;
@property(readonly, copy) XCUIElementQuery *progressIndicators;
@property(readonly, copy) XCUIElementQuery *scrollViews;
@property(readonly, copy) XCUIElementQuery *searchFields;
@property(readonly, copy) XCUIElementQuery *segmentedControls;
@property(readonly, copy) XCUIElementQuery *secureTextFields;
@property(readonly, copy) XCUIElementQuery *sliders;
@property(readonly, copy) XCUIElementQuery *tabBars;
@property(readonly, copy) XCUIElementQuery *tableRows;
@property(readonly, copy) XCUIElementQuery *tableColumns;
@property(readonly, copy) XCUIElementQuery *textFields
@property(readonly, copy) XCUIElementQuery *textViews;
@property(readonly, copy) XCUIElementQuery *webViews;
@property(readonly, copy) XCUIElementQuery *window;;
———————————————————————————————————————
