A numerator-3 simple meter whose rhythm consistently divides into two compound-style groups likely wants 6/8 (or its family), not 3/4

Meter choice communicates intended pulse grouping: 6/8 (two compound beats of three eighths) reads and beams differently from 3/4 (three simple beats) even though both total six eighth-notes per bar. If a piece notated in 3/4 consistently groups its eighth-note content as two threes rather than three twos, it is stylistically mis-notated and should be 6/8.

A melody notated in 3/4 whose durational shape is, bar after bar, one dotted-quarter-equivalent group followed by another, with no rhythmic marker at the true 3/4 beat-2 position — arithmetically valid 3/4, but 6/8 would communicate the intended feel correctly.

Gould, Behind Bars, ch. 'Time signatures', choosing 6/8 vs. 3/4 based on actual beat grouping, not just arithmetic bar length; Read, Music Notation, agrees.

This rule can be decided from pitches, durations and voices — no layout required. A validator can check it before anything is drawn.