HID Keyboard: How to send a TAB character/keypress?

With the below skeleton code I'm trying to send a TAB character (or should it be keypress?) instead of the letter A's. The intention is to control a program which is using the TAB-key to navigate forward, and SHIFT-TAB backward.

If I intepreted the reference at https://www.espruino.com/modules/ble_hid_keyboard.js correctly, "\t" might be TAB, but have not succeeded in replacing the ..KEY.A.. with ..KEY."\t".. or with some other variations.
Can this be done, if so, how?

var kb = require("ble_hid_keyboard");
NRF.setServices(undefined, { hid : kb.report });

function btnPressed() {
  // Send 'a'
  kb.tap(kb.KEY.A, 0, function() {
    // Followed by capital 'A'
    kb.tap(kb.KEY.A, kb.MODIFY.SHIFT);
  });
}

// trigger btnPressed whenever the button is pressed
setWatch(btnPressed, BTN, {edge:"rising",repeat:true,debounce:50});

Ok, partially answering myself.
Using the code from https://github.com/espruino/BangleApps/blob/master/apps/hidkbd/hid-keyboard.js and changing to 0x2b in next = function (cb) { sendHid(0x2b, cb); }; I'm able to simulate TAB by a gesture I've recorded.
But how to simulate SHIFT+TAB?

Ok... found out how to use the first skeleton code, maybe it's of some help to others. So, just needed to add ["\t"], and then MODIFY.SHIFT as per below
kb.tap(kb.KEY["\t"], kb.MODIFY.SHIFT);