Electric field lines begin on positive charges and end on negative ones. How do magnetic field lines differ?

1. Magnetic field lines are continuous, forming closed loops without beginning or end. 2. Outside the magnet they run from the north pole to the south pole, and inside they complete the loop. 3. This is a distinct difference from electric field lines, which begin and end on positive and negative charges. 4. The reason is that north and south poles cannot be separated. 5. If magnetic monopoles existed, field lines would begin and end on them, which is exactly what is never seen. 6. Lines that stopped at a magnet surface would leave the field undefined inside the magnet. _Source: OpenStax College Physics (CC BY 4.0), Ch 22 "Magnetism", section 22.3 Magnetic Fields and Magnetic Field Lines_