How to define this event in IDL file?

I already know how to define this method in IDL: devices.h:

virtual HRESULT STDMETHODCALLTYPE SetGameVoiceMixLevel(
    _In_ double voicePercent,
    _Out_ HSTRING*value) noexcept;

devices.idl:

HRESULT SetGameVoiceMixLevel(
    [in] double voicePercent,
    [out, retval] HSTRING * value1);

But how to define events in IDL? For example this event: devices.h:

virtual HRESULT STDMETHODCALLTYPE OnMessageReceived(
    _In_ UINT64 timestamp,
    _In_ ABI::Windows::Gaming::Input::Custom::GipMessageClass messageClass,
    _In_ BYTE messageId,
    _In_ BYTE sequenceId,
    _In_ UINT32 messageBufferSize,
    _In_reads_bytes_(messageBufferSize) BYTE * messageBuffer) noexcept final override;

Thank you for reading and have a good day!