«Invalid value» error while brackets in chrome.commands - google-chrome-extension

Question

I need hotkeys Alt + ] and Alt + [. I have manifest.json like:
{
...
"commands": {
"nextTrack": {
"suggested_key": {
"default": "Alt+]"
},
"description": "Next track"
},
"previousTrack": {
"suggested_key": {
"default": "Alt+["
},
"description": "Previous track"
},
"toggle": {
"suggested_key": {
"default": "Alt+P"
},
"description": "Toggle pause"
}
},
...
}
When I enable my extension I get:
Could not load extension from '~/project'.
Invalid value for 'commands[1].default': Alt+].
What is way to use that hotkeys?

Answer 1

Only uppercase letters (A-Z) and digits (0-9) are valid values, as you can see by looking at the source code of the chrome.commands API.
If you want to use other characters, inject a content script in every page which binds a keydown event:
document.addEventListener('keydown', function(event) {
if (!event.ctrlKey && event.altKey && event.which === 80/*P*/) {
// Dispatch a custom message, handled by your extension
chrome.runtime.sendMessage('Alt+P');
}
}, true); // <-- True is important
Disadvantages of this method
Keyboard focus must be within a page where the content script is activated. The shortcut will fail if you're inside the Developer tools, omnibar, etc.
Even if you use <all_urls> as a match pattern, it won't work on non http(s) / file / ftp(s) schemes like chrome:, data:, chrome-extension:, about: or the Chrome Web store.
You can run into problems with detecting the [ character, if the keyboard layout does not support it, or uses a different key code.
There's no built-in support for customizing this shortcut (as a user, visit chrome://extensions/, scroll to the bottom and click on "Configure commands" to change the extension's shortcut).
I suggest to pick a different shortcut, or change the way how your extension is controlled (through a page / browser action popup, for instance).