No. It doesn't contain methylxanthines. Carob does not contain caffeine or theobromine which are toxic to dogs. Methylxanthines also may have adverse effects on humans.

Methylxanthines inhibit phospodiesterase which is enzyme that degrade cAMP to AMP. Thus lead to an increase in cAMP

Caffeine does contain a type of xanthine. It is also a trimethylate. It is used as a stimulant and also a bronchodilator and cardiac stimulant. It's chemical formulation is:1,3,7-trimethyl-1H-purine-2,6(3H,7H)-dione

Yes, they are edible. However, they are not very popular because, in fact, they are chocolate covered chickens.

No, cats can't have chocolate. I would suggest not to give them any just to be on the safe side.

Chocolate can contain high amounts of fat and caffeine-like stimulants known as methylxanthines. If ingested in significant amounts, chocolate can potentially produce clinical effects in cats ranging from vomiting and diarrhea to panting, excessive thirst and urination, hyperactivity, abnormal heart rhythm, tremors, seizures and even death in severe cases.

However white chocolate has a significantly lower amount of methylxanthines, which makes it less dangerous. So, if your cat ate some white chocolate, I wouldn't be worried as long as it wasn't a very large amount, but I would check with a vet to be sure. Small amounts may only cause an upset stomach.