I'm an American and I'm thinking of going to Spain for a week or two. I thought that it might be nice to go to Morocco in the middle of the trip for a few days. However, I'm concerned about the visa situation. Would I be allowed to re-enter Spain if I went to Morocco? I know that I can enter Spain without a Visa, but are you allowed to exit the Schengen-zone and then re-enter (all within the 90 days)?