My book is not meant as a reference material, but as a textbook, to be read sequentially. So, chapter titles are just a vague indication of the contents of chapters. However if you download the book, for example in PDF format, you can search for strings. Though, I think that to learn a programming language you really need a textbook, not a reference.
I am a professional programmer, expert in C++, and I am myself still learning Rust. I write something as I learn it. I think that ownership is a rather advanced concept, and should be taught only when the basic concepts have been grasped. By the way, I am now completely rewriting the last chapter.
In general, the book is still a work in progress, and every now and then I change even previous chapters.
I asked for feedback for two reasons: first, I am Italian, and I don't know English language very well; second, I am not a Rust expert, and so I may write something unclear or plainly wrong. Though, to make the language more approachable, I chose to start with a simplified version of the language, and I make it progressively more accurate; so, sometimes, what appears to be an error is just a simplification to make the material more understandable.