When the author of "Mary Poppins" comes to see Walt Disney about making her books into a movie, we learn about her childhood and the inspiration for her characters. She's a rigid sourpuss, immune to the warmth and charms of Mr. Disney, however, and won't even consider the music and animation he wants.
The constant flashbacks to P.L. Travers' childhood are interesting but slow down the main story (and I still don't understand the title). Tom Hanks is utterly lovable as Disney and plays well off Emma Thompson's brittle, control-freak old maid, Travers. It's a lot of fun to see the two pros act together.
There is trivia galore for serious fans of the Mary Poppins movie, but it's lightweight, and inconsequential and more suited as a "extra" on a Mary Poppins DVD, than a full-length film. I enjoyed it but have forgotten most of it already.