localizer driven attributes

[zbraniecki]

In bug https://bugzilla.mozilla.org/show_bug.cgi?id=1608022 we encountered the following issue:

XUL has two attributes - key and keycode. key is used when the shortcut is visible - like ctrl+alt+r. keycode is used when the shortcut is invisible - VK_F9.

The issue is that if in English we use keycode for windows, and any localizer would like to use key instead, Fluent doesn't have a solution for that.

[zbraniecki]

One way to think about it is that if we were to allow localizers to add attributes, and null attributes, then the following would work:

// en-US
foo-windows =
    .keycode = VK_F9

// xx-YY
foo-windows =
    .keycode = None
    .key = R

[zbraniecki]

Additionally, for shortcuts in paticular, having a way to specify a narrow list of options for another attribute - modifiers, would allow the localizer to fully adjust the shortcut and remove a number of cases of ifdefs left in mozilla-central like: https://searchfox.org/mozilla-central/rev/b1e51ad5613ad3d911cf42e3e525885ce2278915/browser/base/content/browser-sets.inc#164-168

// en-US
foo-windows =
    .keycode = VK_F9

// xx-YY
foo-windows =
    .keycode = None
    .key = R
    .modifiers = accel,shift

For such model to work, we'd have to provide meta-information for a CAT tool to allow for UX of selecting from a narrow list of available modifiers - likely with checkboxes.