The thing that Travers would never, ever explain was who exactly Mary Poppins is. And Mary Poppins, as Jane and Michael Banks often lament in the stories, “never explains anything.” Rewatching the film recently, I was pleased to see that she states this herself, when confronted by Mr. Banks; the movie is truer to Travers’ vision that I’d remembered, for if Julie Andrews’ Mary Poppins smiles a lot more than the character in the books, she is almost as strict and no-nonsense. Travers’ Mary Poppins refuses to acknowledge the magical adventures that the children share with her, waxing indignant when they mention having taken tea upside down or floated through the park by the strings of balloons, exploits Mary Poppins seems to regard as undignified. “On his head? A relation of mine on his head? And turning about like a firework display?” she asks wrathfully as they return from one outing on the bus. This attitude seems to bother some contemporary readers. I’ve seen them complain that t...