title: VKAPI_ATTR and VKAPI_CALL macros in Vulkan
body: <p>I have been searching and I still am not sure <strong>what</strong> <code>VKAPI_ATTR</code> and <code>VKAPI_CALL</code> are. I am not sure if they are suppose to be a macro or some fancy C++ function declaration I am not aware of.</p>
  
  <p>What is <code>VKAPI_ATTR void VKAPI_CALL vkCommand(void)</code> offering that <code>void vkCommand(void)</code> doesn't offer?</p>