It will not work with "else if" - with the current implementation it needs to be always executed if the condition is true. Otherwise the execution stops in one of the previous else ifs. For example @ line 2599:

```
} else if ((!this.isMac && ev.altKey) || (this.isMac && ev.metaKey)) {
```

What platform, browser and which kbLayout are you testing out with, other than ee you will only receive 'Not implemented' in your browser log.