Rules glossary
↑ Parent rule: 506.8 Some spells state that they may be cast “only [before/after]…
506.8b A spell that states it may be cast “only before (or after) blockers are declared” is referring to the turn-based action of declaring blockers. It may be cast only before (or after) the declare blockers step begins, regardless of whether any blockers are actually declared. (See rule 509.)
No sub-rules.