According to the latest discussion we only fire non-cancelable
"insertCompositionText" during IME.
Event Order:
1. compositionstart
(2. beforeinput "insertCompositionText"
3. compositionupdate
4.)+ input "insertCompositionText"
5. compositionupdate
2-4 could repeat multiple times.
Note that the implementation should also cover
1. Desktop reverse conversion
2. All platform start composition from non-collapsed selection
3. Android tap and recomposition
Proposal:
https://lists.w3.org/Archives/Public/public-editing-tf/2017Feb/0003.html
Comment 1 by bugdroid1@chromium.org
, Feb 13 2017