When I tried to render DraftJS into an iframe window, for example:

ReactDOM.render(<DraftEditor .../>,
  document
    .getElementById('some_iframe')
    .contentWindow
    .document
    .getElementById('some_inner_element'))

inside the DraftJS functions, there were window, global, document variables, which were global variables, still referenced to the parent window (the window that run the above snippet).
So, global.getSelection, node !== document.documentElement didn't work.

Render components inside iframe is important for isolating CSS especially rem unit.
Looking forward to having a discussion around this. Thank you all!