Google suggested that browsers shouldn't set ctrlKey and altKey to true
for keyboard events during AltGr key is pressed on Windows. We will
follow the new behavior for compatibility with Chromium and better
accessibility for some language users.
https://github.com/w3c/uievents/issues/147
Background: On Windows, AltGr key is mapped to AltRight key by some
keyboard layouts. However, Windows represents AltGraph state with both
Control and Alt modifier states. For example, if user cannot use
AltRight key (e.g., there is no AltRight key), user can emulate it with
pressing both Ctrl and Alt keys. Another example, when user presses
AltGr key, ControlLeft keydown and AltRight keydown are fired, and when
user releases it, CtrlLeft keyup and AltRight keyup are fired.
Firefox, Chrome and Edge set ctrlKey and altKey to true when
getModifierState("AltGraph") returns true. However, web apps cannot
distinguish whether given keydown event will input some characters
strictly. So, if both ctrlKey and altKey are set to false when user
types some character(s) even with AltGr key, the keys won't be handled
as shortcut key on the web apps. The new behavior improves
accessibility of users who use keyboard layout which has AltGr key,
especially when they use different locale's web apps.
When user presses a key with AltGr key to input a character, Gecko has
dispatched:
1. keydown for ControlLeft whose ctrlKey is true.
2. keydown for AltRight whose ctrlKey and altKey are true and
getModifierState("AltGraph") returns true.
3. keydown for the key whose ctrlKey and altKey are true and
getModifierState("AltGraph") returns true.
4. keypress for the key whose ctrlKey and altKey are *false* and
getModifierState("AltGraph") returns true.
5. keyup for the key whose ctrlKey and altKey are true and
getModifierState("AltGraph") returns true.
6. keyup for ControlLeft whose altKey is true.
7. keyup for AltRight (currently, this is not fired due regression of
e10s <https://bugzilla.mozilla.org/show_bug.cgi?id=1435717>)
This becomes:
1. keydown for ControlLeft whose ctrlKey is true.
2. keydown for AltRight whose ctrlKey and altKey are *false* and
getModifierState("AltGraph") returns true.
3. keydown for the key whose ctrlKey and altKey are *false* and
getModifierState("AltGraph") returns true.
4. keypress for the key whose ctrlKey and altKey are false and
getModifierState("AltGraph") returns true.
5. keyup for the key whose ctrlKey and altKey are *false* and
getModifierState("AltGraph") returns true.
6. keyup for ControlLeft whose altKey is *false* but
getModifierState("AltGraph") returns *true*.
7. keyup for AltRight
Additionally, KeyboardEvent.key value for AltRight key becomes
"AltGraph" instead of "Alt" (but KeyboardEvent.keyCode won't be changed
for backward compatibility).
When user types a character with emulating AltGr with ControlLeft and
AltLeft keys:
1. keydown for ControlLeft whose ctrlKey is true.
2. keydown for AltLeft whose ctrlKey and altKey are *true* and
getModifierState("AltGraph") returns *false*.
3. keydown for the key whose ctrlKey and altKey are *false* and
getModifierState("AltGraph") returns *true*.
4. keypress for the key whose ctrlKey and altKey are false and
getModifierState("AltGraph") returns true.
5. keyup for the key whose ctrlKey and altKey are *false* and
getModifierState("AltGraph") returns true.
6. keyup for ControlLeft whose altKey is *true* and also
getModifierState("AltGraph") returns *false*.
7. keyup for AltRight
If the key produces no character when emulating AltGr key press with
Ctrl and Alt keys, its keydown and keyup event's ctrlKey and altKey are
set to *true* and getModifierState("AltGraph") returns false.
In other words, if user emulates AltGr key, only printable key's events
are changed. So, when a key does not input any characters with AltGraph
state, the key combinations can be handled as shortcut keys. Although
any web apps and extensions shouldn't use Control - Alt combination for
shortcut keys at least on Windows.
Note that if active keyboard layout does not have AltGr key,
getModifierState("AltGraph") always returns false (even if both Ctrl and
Alt are pressed).
The bug: https://bugzilla.mozilla.org/show_bug.cgi?id=900750
Target: Firefox 62 or 63.
Chrome has started to release new behavior with 67. And starting from
68, they will switch this behavior permanently.
--
Masayuki Nakano <masay...@d-toybox.com>
Software Engineer, Mozilla
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