Chrome Version: 71.0.3556.0
OS: 11042.0.0

"Vietnamese keyboard (VNI)" currently lacks the standard transform rule whereby typing a diacritic trigger (digits 1-9) a second time cancels a previously assigned diacritic if any. To be precise, cancellation means erasing the diacritic on an applicable preceding letter, if it bears the same one corresponding to the trigger, *and* type the trigger digits literally.

This is highly expected by any average users. "Double-type" to "temporarily disable" Vietnamese VNI is standard and extremely helpful, to avoid the need of really turning off the whole IME just to type a couple of tokens that contain the characters "borrowed" by the IME for use as diacritic triggers (e.g. passwords or cryptic things with alphanumerics, or just neologisms).

Which letter exactly to apply the cancellation depends on whether strict or flexible trigger mode is active. Also, this applies to all kinds of diacritics, i.e. both tone marks and letter modifiers.

Non-exhaustive examples:
- type "ca11" -> expect "ca1", currently get "cá1"
- type "tra62n6" -> expect "tràn6", currently get "trần6"

NOTE: When flexible trigger is active, this should work correctly for *all* cases as per Vietnamese orthography, with regard to diacritic placement and syllable structure, not just the minimal simplistic examples above. The VNI rule itself, if implemented correctly as such, is linguistically sound and thus consistent and reliable.