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# Event Handling System
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Comprehensive event handling system with Windows-specific enhancements including keyboard navigation, mouse interactions, focus management, and native event integration.
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## Capabilities
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### Keyboard Events
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#### Enhanced Keyboard Support
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Windows-specific keyboard event handling with support for modifier keys, key combinations, and navigation patterns.
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```typescript { .api }
13
/**
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 * Event phase enumeration for keyboard and mouse events
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 */
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namespace EventPhase {
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  export const None = 0;
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  export const Capturing = 1;
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  export const AtTarget = 2;
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  export const Bubbling = 3;
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}
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/**
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 * React Native synthetic event wrapper
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 */
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interface NativeSyntheticEvent<T> {
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  nativeEvent: T;
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  currentTarget: EventTarget;
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  target: EventTarget;
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  bubbles: boolean;
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  cancelable: boolean;
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  defaultPrevented: boolean;
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  eventPhase: number;
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  isTrusted: boolean;
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  preventDefault(): void;
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  stopPropagation(): void;
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  timeStamp: number;
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  type: string;
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}
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/**
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 * Windows keyboard event interface with comprehensive key information
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 * Supports modifier keys, key codes, and event phases
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 */
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interface INativeKeyboardEvent {
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  /** Alt key pressed state */
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  altKey: boolean;
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  /** Ctrl key pressed state */
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  ctrlKey: boolean;
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  /** Meta key (Windows key) pressed state */
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  metaKey: boolean;
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  /** Shift key pressed state */
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  shiftKey: boolean;
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  /** Key identifier string */
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  key: string;
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  /** Physical key code */
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  code: string;
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  /** Event phase (capturing, at target, bubbling) */
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  eventPhase: EventPhase.None | EventPhase.Capturing | EventPhase.AtTarget | EventPhase.Bubbling;
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}
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type IKeyboardEvent = NativeSyntheticEvent<INativeKeyboardEvent>;
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/**
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 * Handled keyboard event configuration interface
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 */
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interface IHandledKeyboardEvent {
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  /** Alt key requirement */
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  altKey?: boolean;
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  /** Ctrl key requirement */
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  ctrlKey?: boolean;
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  /** Meta key requirement */
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  metaKey?: boolean;
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  /** Shift key requirement */
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  shiftKey?: boolean;
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  /** Physical key code to handle */
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  code: string;
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  /** Event phase to handle */
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  handledEventPhase?: EventPhase.Capturing | EventPhase.Bubbling;
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}
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/**
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 * Keyboard event handlers for Windows components
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 */
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interface KeyboardEventHandlers {
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  /** Key down event handler */
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  onKeyDown?: (args: IKeyboardEvent) => void;
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  /** Key up event handler */
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  onKeyUp?: (args: IKeyboardEvent) => void;
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  /** Capture phase key down handler */
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  onKeyDownCapture?: (args: IKeyboardEvent) => void;
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  /** Capture phase key up handler */
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  onKeyUpCapture?: (args: IKeyboardEvent) => void;
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  /** Array of handled keyboard events for onKeyDown */
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  keyDownEvents?: IHandledKeyboardEvent[];
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  /** Array of handled keyboard events for onKeyUp */
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  keyUpEvents?: IHandledKeyboardEvent[];
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}
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```
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**Usage Examples:**
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```typescript
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import React from 'react';
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import { View, Text } from 'react-native-windows';
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const KeyboardExample: React.FC = () => {
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  const handleKeyDown = (event: IKeyboardEvent) => {
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    const { key, ctrlKey, shiftKey, altKey } = event.nativeEvent;
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    // Handle specific key combinations
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    if (ctrlKey && key === 's') {
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      console.log('Save shortcut pressed');
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      event.preventDefault();
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    } else if (key === 'Enter') {
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      console.log('Enter key pressed');
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    } else if (key === 'Escape') {
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      console.log('Escape key pressed');
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    }
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    // Handle modifier combinations
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    if (ctrlKey && shiftKey && key === 'p') {
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      console.log('Command palette shortcut');
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    }
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  };
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  return (
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    <View
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      tabIndex={0}
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      onKeyDown={handleKeyDown}
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      keyDownEvents={[
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        { code: 'Enter' },
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        { code: 'Escape' },
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        { code: 'Space' },
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        { code: 'ArrowUp' },
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        { code: 'ArrowDown' }
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      ]}
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      style={{ padding: 16, backgroundColor: '#f0f0f0' }}
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    >
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      <Text>Press keys to interact</Text>
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    </View>
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  );
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};
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```
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### Mouse Events
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#### Mouse Interaction Support
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Comprehensive mouse event handling with button states, coordinates, and modifier key support.
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```typescript { .api }
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/**
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 * Windows mouse event interface with detailed interaction information
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 * Provides button states, coordinates, and modifier keys
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 */
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type INativeMouseEvent = {
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  /** Target element reference */
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  target: number;
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  /** Mouse event identifier */
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  identifier: number;
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  /** X coordinate relative to page */
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  pageX: number;
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  /** Y coordinate relative to page */
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  pageY: number;
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  /** X coordinate relative to the element */
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  locationX: number;
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  /** Y coordinate relative to the element */
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  locationY: number;
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  /** Event timestamp */
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  timestamp: number;
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  /** Pointer type (mouse, pen, touch) */
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  pointerType: string;
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  /** Pressure force applied */
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  force: number;
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  /** Left mouse button pressed state */
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  isLeftButton: boolean;
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  /** Right mouse button pressed state */
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  isRightButton: boolean;
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  /** Middle mouse button pressed state */
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  isMiddleButton: boolean;
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  /** Barrel button pressed state (pen) */
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  isBarrelButtonPressed: boolean;
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  /** Horizontal scroll wheel active */
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  isHorizontalScrollWheel: boolean;
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  /** Eraser mode active (pen) */
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  isEraser: boolean;
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  /** Shift key pressed state */
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  shiftKey: boolean;
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  /** Ctrl key pressed state */
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  ctrlKey: boolean;
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  /** Alt key pressed state */
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  altKey: boolean;
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};
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type IMouseEvent = NativeSyntheticEvent<INativeMouseEvent>;
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/**
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 * Mouse event handlers for Windows components
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 */
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interface MouseEventHandlers {
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  /** Mouse enter event handler */
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  onMouseEnter?: (args: IMouseEvent) => void;
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  /** Mouse leave event handler */
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  onMouseLeave?: (args: IMouseEvent) => void;
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}
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```
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**Usage Examples:**
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```typescript
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import React, { useState } from 'react';
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import { View, Text } from 'react-native-windows';
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const MouseExample: React.FC = () => {
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  const [mouseInfo, setMouseInfo] = useState('');
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  const [isHovered, setIsHovered] = useState(false);
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  const handleMouseEnter = (event: IMouseEvent) => {
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    setIsHovered(true);
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    setMouseInfo(`Mouse entered at (${event.nativeEvent.pageX}, ${event.nativeEvent.pageY})`);
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  };
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  const handleMouseLeave = () => {
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    setIsHovered(false);
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    setMouseInfo('Mouse left');
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  };
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  return (
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    <View
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      onMouseEnter={handleMouseEnter}
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      onMouseLeave={handleMouseLeave}
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      style={{
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        padding: 20,
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        backgroundColor: isHovered ? '#e3f2fd' : '#f5f5f5',
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        borderRadius: 8,
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        margin: 16,
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      }}
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    >
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      <Text>Mouse interaction area</Text>
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      <Text style={{ fontSize: 12, color: '#666', marginTop: 8 }}>
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        {mouseInfo || 'Move mouse over this area'}
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      </Text>
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    </View>
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  );
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};
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```
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### Focus Events
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#### Focus Management System
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Windows focus management with accessibility support and keyboard navigation.
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```typescript { .api }
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/**
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 * Focus event interface for accessibility and navigation
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 */
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interface IFocusEvent {
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  /** Target element that received/lost focus */
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  target: any;
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  /** Related target (element losing/gaining focus) */
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  relatedTarget?: any;
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  /** Event timestamp */
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  timeStamp: number;
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}
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/**
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 * Focus event handlers
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 */
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interface FocusEventHandlers {
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  /** Focus gained handler */
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  onFocus?: (event: { nativeEvent: IFocusEvent }) => void;
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  /** Focus lost handler */
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  onBlur?: (event: { nativeEvent: IFocusEvent }) => void;
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  /** Focus gained (capture phase) */
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  onFocusCapture?: (event: { nativeEvent: IFocusEvent }) => void;
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  /** Focus lost (capture phase) */
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  onBlurCapture?: (event: { nativeEvent: IFocusEvent }) => void;
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}
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/**
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 * Focus management properties
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 */
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interface FocusProps {
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  /** Tab navigation index */
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  tabIndex?: number;
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  /** Enable focus ring visibility */
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  enableFocusRing?: boolean;
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  /** Auto focus on mount */
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  autoFocus?: boolean;
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  /** Focus on click/press */
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  focusable?: boolean;
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}
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```
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**Usage Examples:**
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```typescript
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import React, { useState, useRef } from 'react';
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import { View, Text, Pressable } from 'react-native-windows';
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const FocusExample: React.FC = () => {
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  const [focusedElement, setFocusedElement] = useState<string>('');
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  const buttonRefs = useRef<Array<React.RefObject<any>>>([]);
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  const handleFocus = (elementName: string) => (event: { nativeEvent: IFocusEvent }) => {
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    setFocusedElement(elementName);
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    console.log(`${elementName} gained focus`);
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  };
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  const handleBlur = (elementName: string) => () => {
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    console.log(`${elementName} lost focus`);
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  };
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  const handleKeyDown = (event: { nativeEvent: IKeyboardEvent }) => {
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    const { key } = event.nativeEvent;
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    // Arrow key navigation
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    if (key === 'ArrowDown' || key === 'ArrowRight') {
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      // Move to next focusable element
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      const currentIndex = focusedElement ? parseInt(focusedElement.split(' ')[1]) - 1 : -1;
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      const nextIndex = Math.min(currentIndex + 1, buttonRefs.current.length - 1);
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      buttonRefs.current[nextIndex]?.current?.focus();
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    } else if (key === 'ArrowUp' || key === 'ArrowLeft') {
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      // Move to previous focusable element
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      const currentIndex = focusedElement ? parseInt(focusedElement.split(' ')[1]) - 1 : buttonRefs.current.length;
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      const prevIndex = Math.max(currentIndex - 1, 0);
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      buttonRefs.current[prevIndex]?.current?.focus();
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    }
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  };
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  return (
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    <View onKeyDown={handleKeyDown} style={{ padding: 16 }}>
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      <Text style={{ marginBottom: 16 }}>
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        Currently focused: {focusedElement || 'None'}
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      </Text>
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      {[1, 2, 3].map((num) => {
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        const ref = React.createRef();
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        buttonRefs.current[num - 1] = ref;
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        return (
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          <Pressable
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            key={num}
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            ref={ref}
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            tabIndex={num}
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            enableFocusRing={true}
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            onFocus={handleFocus(`Button ${num}`)}
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            onBlur={handleBlur(`Button ${num}`)}
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            style={{
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              padding: 12,
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              backgroundColor: focusedElement === `Button ${num}` ? '#0078d4' : '#f0f0f0',
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              marginBottom: 8,
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              borderRadius: 4,
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            }}
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          >
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            <Text style={{
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              color: focusedElement === `Button ${num}` ? 'white' : 'black'
361
            }}>
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              Button {num} (Tab Index: {num})
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            </Text>
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          </Pressable>
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        );
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      })}
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    </View>
368
  );
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};
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```
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### Touch and Gesture Events
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#### Touch Event System
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Enhanced touch event handling with Windows-specific touch and pen support.
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378
```typescript { .api }
379
/**
380
 * Touch event interface with multi-touch support
381
 */
382
interface ITouchEvent {
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  /** Array of changed touch points */
384
  changedTouches: Touch[];
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  /** Touch identifier */
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  identifier: number;
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  /** X coordinate relative to component */
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  locationX: number;
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  /** Y coordinate relative to component */
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  locationY: number;
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  /** X coordinate relative to page */
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  pageX: number;
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  /** Y coordinate relative to page */
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  pageY: number;
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  /** Target element */
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  target: number;
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  /** Event timestamp */
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  timestamp: number;
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  /** All active touch points */
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  touches: Touch[];
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}
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interface Touch {
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  /** Unique touch identifier */
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  identifier: number;
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  /** X coordinate relative to component */
407
  locationX: number;
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  /** Y coordinate relative to component */
409
  locationY: number;
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  /** X coordinate relative to page */
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  pageX: number;
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  /** Y coordinate relative to page */
413
  pageY: number;
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  /** Target element */
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  target: number;
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  /** Touch timestamp */
417
  timestamp: number;
418
  /** Touch force (pressure) */
419
  force?: number;
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  /** Touch radius */
421
  majorRadius?: number;
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  /** Touch radius */
423
  minorRadius?: number;
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}
425

426
/**
427
 * Touch event handlers
428
 */
429
interface TouchEventHandlers {
430
  /** Touch start handler */
431
  onTouchStart?: (event: { nativeEvent: ITouchEvent }) => void;
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  /** Touch move handler */
433
  onTouchMove?: (event: { nativeEvent: ITouchEvent }) => void;
434
  /** Touch end handler */
435
  onTouchEnd?: (event: { nativeEvent: ITouchEvent }) => void;
436
  /** Touch cancel handler */
437
  onTouchCancel?: (event: { nativeEvent: ITouchEvent }) => void;
438
}
439
```
440

441
### Event Phase Management
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443
#### Event Phase Control
444

445
Windows-specific event phase management for capture and bubble phases.
446

447
```typescript { .api }
448
/**
449
 * Event phase enumeration for Windows event handling
450
 */
451
enum EventPhase {
452
  /** No event phase */
453
  None = 0,
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  /** Capture phase (top-down) */
455
  Capturing = 1,
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  /** At target element */
457
  AtTarget = 2,
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  /** Bubble phase (bottom-up) */
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  Bubbling = 3,
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}
461

462
/**
463
 * Handled event phase enumeration
464
 */
465
enum HandledEventPhase {
466
  /** No handling */
467
  None = 0,
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  /** Handle in capture phase */
469
  Capturing = 1,
470
  /** Handle at target */
471
  AtTarget = 2,
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  /** Handle in bubble phase */
473
  Bubbling = 3,
474
}
475

476
/**
477
 * Event handler configuration with phase control
478
 */
479
interface EventHandlerConfig {
480
  /** Event phase to handle */
481
  handledEventPhase?: HandledEventPhase;
482
  /** Stop event propagation */
483
  stopPropagation?: boolean;
484
  /** Prevent default behavior */
485
  preventDefault?: boolean;
486
}
487
```
488

489
**Usage Examples:**
490

491
```typescript
492
import React from 'react';
493
import { View, Text } from 'react-native-windows';
494

495
const EventPhaseExample: React.FC = () => {
496
  const handleParentKeyDown = (event: { nativeEvent: IKeyboardEvent }) => {
497
    console.log('Parent received key event in:',
498
      event.nativeEvent.eventPhase === EventPhase.Capturing ? 'Capture' : 'Bubble');
499
  };
500

501
  const handleChildKeyDown = (event: { nativeEvent: IKeyboardEvent }) => {
502
    console.log('Child handling key event:', event.nativeEvent.key);
503

504
    // Stop propagation to parent
505
    if (event.nativeEvent.key === 'Escape') {
506
      event.stopPropagation();
507
    }
508
  };
509

510
  return (
511
    <View
512
      tabIndex={0}
513
      onKeyDown={handleParentKeyDown}
514
      onKeyDownCapture={handleParentKeyDown} // Capture phase
515
      style={{ padding: 20, backgroundColor: '#f0f0f0' }}
516
    >
517
      <Text>Parent Container (receives events in capture and bubble)</Text>
518

519
      <View
520
        tabIndex={0}
521
        onKeyDown={handleChildKeyDown}
522
        style={{
523
          padding: 16,
524
          marginTop: 16,
525
          backgroundColor: '#e3f2fd',
526
          borderRadius: 4
527
        }}
528
      >
529
        <Text>Child Element (press Escape to stop propagation)</Text>
530
      </View>
531
    </View>
532
  );
533
};
534
```
535

536
### Custom Event Handling
537

538
#### Advanced Event Patterns
539

540
Complex event handling patterns for Windows applications.
541

542
```typescript { .api }
543
/**
544
 * Custom event handler utilities
545
 */
546
interface EventUtils {
547
  /** Throttle event handler */
548
  throttle<T extends (...args: any[]) => any>(
549
    func: T,
550
    delay: number
551
  ): T;
552

553
  /** Debounce event handler */
554
  debounce<T extends (...args: any[]) => any>(
555
    func: T,
556
    delay: number
557
  ): T;
558

559
  /** Combine multiple event handlers */
560
  combine<T>(...handlers: Array<(event: T) => void>): (event: T) => void;
561
}
562
```
563

564
**Usage Examples:**
565

566
```typescript
567
import React, { useCallback, useMemo } from 'react';
568
import { View, Text } from 'react-native-windows';
569

570
const CustomEventExample: React.FC = () => {
571
  // Debounced search handler
572
  const debouncedSearch = useCallback(
573
    debounce((query: string) => {
574
      console.log('Searching for:', query);
575
    }, 300),
576
    []
577
  );
578

579
  // Throttled scroll handler
580
  const throttledScroll = useCallback(
581
    throttle((event: any) => {
582
      console.log('Scroll position:', event.nativeEvent.contentOffset);
583
    }, 100),
584
    []
585
  );
586

587
  // Combined key handler
588
  const combinedKeyHandler = useMemo(
589
    () => combine(
590
      (event: { nativeEvent: IKeyboardEvent }) => {
591
        // Log all keys
592
        console.log('Key pressed:', event.nativeEvent.key);
593
      },
594
      (event: { nativeEvent: IKeyboardEvent }) => {
595
        // Handle shortcuts
596
        if (event.nativeEvent.ctrlKey && event.nativeEvent.key === 'f') {
597
          console.log('Find shortcut');
598
        }
599
      }
600
    ),
601
    []
602
  );
603

604
  return (
605
    <View
606
      tabIndex={0}
607
      onKeyDown={combinedKeyHandler}
608
      style={{ padding: 16 }}
609
    >
610
      <Text>Advanced event handling example</Text>
611
    </View>
612
  );
613
};
614

615
// Utility implementations
616
function debounce<T extends (...args: any[]) => any>(func: T, delay: number): T {
617
  let timeoutId: NodeJS.Timeout;
618
  return ((...args: any[]) => {
619
    clearTimeout(timeoutId);
620
    timeoutId = setTimeout(() => func.apply(this, args), delay);
621
  }) as T;
622
}
623

624
function throttle<T extends (...args: any[]) => any>(func: T, delay: number): T {
625
  let inThrottle: boolean;
626
  return ((...args: any[]) => {
627
    if (!inThrottle) {
628
      func.apply(this, args);
629
      inThrottle = true;
630
      setTimeout(() => inThrottle = false, delay);
631
    }
632
  }) as T;
633
}
634

635
function combine<T>(...handlers: Array<(event: T) => void>): (event: T) => void {
636
  return (event: T) => {
637
    handlers.forEach(handler => handler(event));
638
  };
639
}
640
```
641

642
## Windows Event Patterns
643

644
### Keyboard Navigation
645

646
```typescript
647
// Standard Windows keyboard navigation
648
const keyboardNavigation = {
649
  // Tab navigation
650
  'Tab': () => focusNext(),
651
  'Shift+Tab': () => focusPrevious(),
652

653
  // Arrow navigation
654
  'ArrowDown': () => moveDown(),
655
  'ArrowUp': () => moveUp(),
656
  'ArrowLeft': () => moveLeft(),
657
  'ArrowRight': () => moveRight(),
658

659
  // Action keys
660
  'Enter': () => activate(),
661
  'Space': () => activate(),
662
  'Escape': () => cancel(),
663

664
  // Windows shortcuts
665
  'Ctrl+a': () => selectAll(),
666
  'Ctrl+c': () => copy(),
667
  'Ctrl+v': () => paste(),
668
  'Ctrl+z': () => undo(),
669
  'F1': () => showHelp(),
670
  'Alt+F4': () => closeWindow(),
671
};
672
```
673

674
### Accessibility Events
675

676
```typescript
677
// Accessibility-focused event handling
678
const accessibilityEvents = {
679
  onFocus: (event) => {
680
    // Announce focus change to screen readers
681
    announceForAccessibility(`Focused on ${getAccessibilityLabel(event.target)}`);
682
  },
683

684
  onKeyDown: (event) => {
685
    // Handle accessibility shortcuts
686
    if (event.nativeEvent.key === 'F6') {
687
      // Move between major UI sections
688
      moveToNextSection();
689
    }
690
  },
691

692
  onMouseEnter: (event) => {
693
    // Provide hover feedback for screen readers
694
    if (isScreenReaderActive()) {
695
      announceHoverContent(event.target);
696
    }
697
  },
698
};
699
```
700

701
### High Performance Events
702

703
```typescript
704
// Optimized event handling for performance
705
const highPerformanceEvents = {
706
  // Use native driver for animations
707
  onScroll: Animated.event(
708
    [{ nativeEvent: { contentOffset: { y: scrollY } } }],
709
    { useNativeDriver: true }
710
  ),
711

712
  // Minimize re-renders with useCallback
713
  onPress: useCallback((event) => {
714
    handlePress(event);
715
  }, [dependencies]),
716

717
  // Batch state updates
718
  onMultipleEvents: (events) => {
719
    unstable_batchedUpdates(() => {
720
      events.forEach(handleEvent);
721
    });
722
  },
723
};
724
```