Optional
Predicate consulted on each move while phase === 'pending'. Return true to transition to 'active'. The transition fires onActivate before the triggering move's onMove. When omitted, gesture activates at start().
Predicate consulted on each move while phase === 'pending'. Return true to transition to 'active'. The transition fires onActivate before the triggering move's onMove. When omitted, gesture activates at start().