The unique identifier of the main frame. It's the same kind of ID as
with the FrameId in CoreWebView2Frame and via CoreWebView2FrameInfo.
Note that FrameId may not be valid if CoreWebView2 has not done
any navigation. It's safe to get this value during or after the first
ContentLoading event. Otherwise, it could return the invalid frame Id 0.
The unique identifier of the main frame. It's the same kind of ID as with the FrameId in CoreWebView2Frame and via CoreWebView2FrameInfo. Note that FrameId may not be valid if CoreWebView2 has not done any navigation. It's safe to get this value during or after the first ContentLoading event. Otherwise, it could return the invalid frame Id 0.