An accidental must clear a minimum gap from its own notehead and from the previous note's glyphs

An accidental sits immediately to the left of its notehead with a small fixed clearance — close enough to read as attached, never touching the notehead or overlapping a preceding note's stem/flag/dot.

A dense passage compresses two adjacent notes so far that the second note's sharp sign overlaps the first note's dot-of-augmentation or flag.

Gould, Behind Bars, ch. 'Accidentals'; Ross, The Art of Music Engraving gives an explicit minimum accidental-to-notehead spacing figure for a given staff size.

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