Gertrude Stein's Tender Buttons

The image above is a detail from Pablo Picasso's portrait of Gertrude Stein (1906-7). Stein was one of his first collectors and supporters. Here's a short video discussion of Picasso's portrayal of Stein by two art historians.

One of Gertrude Stein's most well-known books is Tender Buttons. What exactly is this text? Is it nonsense? Non-sense? Why objects, food, and rooms?