A tuplet bracket is suppressed (numeral alone shown) when every member note already carries a beam; shown when any member lacks one

When every note of a tuplet is joined by a beam, the beam already shows the grouping, so many engraving conventions omit the bracket and show only the ratio numeral, reserving the full bracket for tuplets containing an unbeamed note, a rest, or notes too long to beam.

Gould, Behind Bars, ch. 'Tuplets', bracket-vs-numeral-alone convention; this is also the confirmed, exact behavior of VexFlow's own `Tuplet` class (node_modules/vexflow/src/tuplet.ts): `this.bracketed = notes.some(note => !note.hasBeam)` when `options.bracketed` is not explicitly set — bracket shown unless EVERY member note has a beam. Ross, The Art of Music Engraving, documents the same convention as standard hand-engraving practice. Some house styles (and pedagogical material generally) prefer ALWAYS showing the bracket regardless of beaming for maximum clarity with beginners — a legitimate, deliberate divergence, not an error.

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