Research? Plenty. You’d have to google to find and look as recommended by Natialie above in the archives here. The big question being debated is what kind is best and how long it lasts (newest studies show 1 hour). There is plenty of research showing dynamic ROM drills/exercises are the ONLY type of stretching that MAY help prevent injury. Also that static stretching is best done after a workout or athletics, when muscles are warm. Plenty of research supporting fascia release and proprioceptive neuromuscular facilitation (PNF stretching).
That said: if working with a “hyperflexible” client, I’d forgo most stretching except for what is needed for that person’s thoracic spine and hips.