function _keyShouldApply(event) {
	if (event.key === "Enter") return 1;
	if (event.key === "Tab") return 1;
	if (event.key === "Backspace") return -1;
	if (event.key === "ArrowLeft") return -1;
	if (event.key === "ArrowRight") return 1;
	if (event.key === "ArrowUp") return -16;
	if (event.key === "ArrowDown") return 16;
	return null;
}
Determines if a key event should result in a byte index change.

@param {KeyboardEvent} event - The keyboard event.
@returns {number|null} - The byte index change or null.