I want to enable only keyboard input of keys: `+` `-` `[0-9]` `,` and disable rest of keys input in `edittext` box.  

Also if `edittext` has already any `,` character, I want to block any further key `,` input.

```
var mainWindow = new Window("dialog");
var edittext = mainWindow.add("edittext", undefined, 0);
edittext.characters = 40;

edittext.onChanging = function() {
    //enabling only input keys [0-9,-+] from keyboard
}

mainWindow.show();

```

Thanks in advance.