$ cat /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/
  System/Library/Frameworks/Virtualization.framework/Headers/VZBootLoader.h 
  //
  //  VZBootLoader.h
  //  Virtualization
  //
  //  Copyright © 2019 Apple Inc. All rights reserved.
  //

  #import <Virtualization/VZDefines.h>
  
  NS_ASSUME_NONNULL_BEGIN
  
  /*!
   @abstract Base class of boot loader configuration.
   @discussion
       VZVirtualMachineConfiguration requires a boot loader defining how to start the virtual machine.
       VZBootLoader is the abstract base class of boot loader definitions.
  
       Don't instantiate VZBootLoader directly, instead you should use one of its subclasses.
  
   @see VZLinuxBootLoader.
   */
  VZ_EXPORT API_AVAILABLE(macos(11.0))
  @interface VZBootLoader : NSObject <NSCopying>
  
  + (instancetype)new NS_UNAVAILABLE;
  - (instancetype)init NS_UNAVAILABLE;
  
  @end
  
  NS_ASSUME_NONNULL_END