EXPLAINED: What happens if you overstay your 90 day limit in Spain?

Visitors to Spain from non-EU countries are subject to the 90-day rule, which states that they can only stay for 90 days out of 180. But how strictly is this rule enforced - and what happens if you end up overstaying?

EXPLAINED: What happens if you overstay your 90 day limit in Spain?
Visitors to Spain from non-EU countries are subject to the 90-day rule, which states that they can only stay for 90 days out of 180. But how strictly is this rule enforced - and what happens if you end up overstaying?