A slur must not visually overlap a dynamic marking, articulation mark, or another slur below/above the staff

When a slur shares vertical space with a dynamic or articulation mark on the same side of the staff, engraving convention nudges one or the other further away — never allows visual collision.

Gould's chapters on 'Dynamics' and 'Articulation marks' both note that slurs/phrase marks and these other marks must be spaced to avoid collision when they occupy the same region.

This rule is about where marks land on the page, so it can only be judged after engraving. Collision and spacing faults live here.