7.2.16 The fn:zero-or-one, fn:one-or-more, and fn:exactly-one functions

"For example"
    Start a new para with this sentence?

"the function always return at most one book element"
    s/return/returns/

"However, the static typing feature cannot infers"
    s/infers/infer/

"will return a static type error at compile time"
    1) You don't "return" an error, you "raise" it.
    2) 'static error' and 'type error' are distinct.
    3) "compile time" is not defined.
    So change to:
        "will raise a type error during static type analysis"