What is the mandatory driver action required by the octagonal red STOP sign (Znak II-2 / 'Obavezno zaustavljanje')?

1. Come to a complete physical standstill at the marked stop line (or intersection edge) and yield to all vehicles on the priority road
2. Slow down to 10 km/h and proceed without stopping if no cars are visible
3. Stop only if approaching traffic is within 20 metres
4. Stop only when an oncoming driver sounds their horn