Question on millis() and how it disables interrupts

Using Arduino Programming Questions
1

So I'm trying to understand how calling millis() and delay() (which calls micros()) interacts with other interrupts in the system.

unsigned long millis()
{
	unsigned long m;
	uint8_t oldSREG = SREG;

	// disable interrupts while we read timer0_millis or we might get an
	// inconsistent value (e.g. in the middle of a write to timer0_millis)
	cli();
	m = timer0_millis;
	SREG = oldSREG;

	return m;
}

This function calls cli() to disable interrupts, but it never calls sei() to re-enable interrupts. The same happens inside the micros() function. How do interrupts get re-enabled? Is the application that calls millis() or delay() responsible for calling sei() after the function call?

2

Bit 7 of SREG is the global interrupt bit.

The function stores the value of SREG, disables the bit, then returns the bit to its previous state.