A tuplet beam may legitimately span what would otherwise be two simple-meter beat groups

A tuplet of note values that would not normally take a beam on their own (e.g., a quarter-note triplet, where quarter notes are unbeamed) is joined by a plain beam so the figure reads as one rhythmic unit — this beam is permitted to cross the notional beat division the tuplet itself creates, because the tuplet bracket/beam IS the higher-level grouping signal.

N/A as a fault — documents correct behavior that must not be mistakenly flagged by the barline/beat-grid checks above.

Gould, Behind Bars, ch. Beaming and ch. Tuplets — a beamed tuplet spanning the underlying pulse is standard and necessary notation, not an error.

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