What is the theme in The Princess Bride by Rob Reiner?

The enduring strength of true love is the central theme of this story. The cover of the book tells the reader that S. Morgenstern is presenting a "classic tale of true love." Immediately the reader assumes that the true love refers to that between a man and a woman. However, in The Princess Bride there are several kinds of true love and the point of the story is "true" love. True as used in The Princess Bride refers to purity. The more pure and unadulterated one's love for another is, the more true the love.