Also "to access" is cleaner than "for accessing"

grammatical: "Here's" should be "Here are", "rules" is plural.
stylistic: "rules for" is more idiomatic than "rules about".
grammatical: No verb in "One or the other"; changed to "It's one or the other".
code: added implied `fn main() { ... }` because it is referenced in "note: previous borrow ends here"
semantic: "But" seems like the wrong word here, there is now, contrast, only further explanation. "so", "thus" or "therefor" is clearer.
grammatical: Another misuse of "Here's", should be "Here are" (or possibly "Here're").
grammatical: "use" should be capitalized. All other subheadings capitalize the first word.

two terms (input lifetime and output lifetime) so "term" needs to be plural.

no reason for a long comment in a code block when we could take it out, especially since it looks like it's using markdown (`struct`, `&` and `lvl`).