A tuplet's bracket and numeral must sit on the side of the beam/stems, not always above the staff

The tuplet bracket and numeral are placed on the side the beam occupies — above the notes when stems point up (as the beam does), below when stems point down — mirroring how beam placement itself follows stem direction. For an unbeamed or mixed-stem group the placement follows the majority stem direction, defaulting above when there is no forced direction.

Gould, Behind Bars, ch. 'Tuplets', bracket/numeral placement on the beam side; this is exactly what VexFlow's `Tuplet.LOCATION_TOP`/`LOCATION_BOTTOM` option exists to control, defaulting to `LOCATION_TOP` when unset.

This rule needs the notated content and the rendered result together — the score says what should happen, the page says whether it did.