Intent to Ship: Fixes to modifier flags on AltGraph-shifted keydown/keypress/keyup events.
Wez
Contact emails
inpu...@chromium.org | w...@chromium.org
Spec & Bugs
At present the expected behaviour of AltGraph on Windows is not well specified (see Summary).
Chromium user-reported bug that illustrates the issues this causes:
https://bugs.chromium.org/p/chromium/issues/detail?id=25503
DOM UI Events bug tracking improvements to the specification of AltGraph behaviour:
https://github.com/w3c/uievents/issues/147
Summary
Under Windows the right-hand Alt key serves as AltGraph (aka ISO-Level-3-Shift) under some layouts (e.g. many European language layouts), to allow an additional set of printable-characters to be generated.
Internally Windows implements AltGraph as Control+Alt.
DOM UI Events does not currently specify/clarify how this implementation detail should be handled by user agents.
At present, Chrome faithfully translates the Windows Control and Alt modifier bits to their DOM counterparts in input event flags, and if both are set then it additionally sets the AltGraph modifier flag. This leads to confusion when handling AltGraph-shifted keyboard input.
We propose to enable the following new behaviour:
If the right-hand Alt key is pressed, then under AltGraph layouts, set the AltGraph modifer.
If Control+Alt are set on a key event that generates a printable character, set AltGraph.
When AltGraph is set, clear the Control and Alt modifier flags.
Is this feature supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?
Yes - This is a fix to the AltGraph modifier under Windows, to better match other platforms.
Demo link
https://w3c.github.io/uievents/tools/key-event-viewer.html
includes a getModifierState() column under which AltGraph will be listed, if set on an event.
Risks
Interoperability and Compatibility
We believe the main risk is user expectations of sites which make use of Control+Alt modified key sequences as shortcuts. Users with AltGraph keyboard layouts configured may then believe that the sequence is triggered by the AltGraph key (since that used to set Control+Alt as well as AltGraph). Users will be able to reach those sequences by pressing left-Alt plus either Control key, instead.
Compatibility should generally be improved, since we are making Control/Alt/AltGraph modifiers easier for sites to distinguish under Windows, by making the behaviour consistent with Chrome on other platforms.
Edge: No signals
Firefox:Public support
Safari: N/A
Web developers: No signals
Is this feature fully tested by web-platform-tests? Link to test suite results from wpt.fyi.
This change is a platform-specific implementation detail of Chrome’s input pipeline, sitting below the level at which web-platform tests can typically drive the browser. We do not believe that web-platform tests are feasible in this case.
Entry on the feature dashboard:
https://www.chromestatus.com/feature/5059438092222464
Rick Byers
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Wez
So this would be changing from matching Edge's behavior in this regard to doing something different? That seems like something to at least get Microsoft input on. +patket@ (input/interop PM) who may be able to comment.
Do you have a link to the public support from Firefox?
PhistucK
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