fix(test): fix doc test
@@ -3050,14 +3050,18 @@ impl<'help> Arg<'help> {
/// assert_eq!(m.value_of("flag"), Some("env"));
/// ```
///
- /// In this example, we show the flag being raised but with no value because
- /// of not setting [`Arg::takes_value(true)`]:
+ /// In this example, because [`Arg::takes_value(false)`] (by default),
+ /// `prog` is a flag that only accepts optional, case-insensitive boolean literals.
+ /// A `true` literal is `y`, `yes`, `t`, `true`, `on` or `1`;
+ /// a `false` literal is `n`, `no`, `f`, `false`, `off` or `0`.
+ /// An absent environment variable will be considered as `false`.
+ /// Anything else will cause a parsing error.
///
/// ```rust
/// # use std::env;
/// # use clap::{App, Arg};
///
- /// env::set_var("MY_FLAG", "env");
+ /// env::set_var("MY_FLAG", "true");
///
/// let m = App::new("prog")
/// .arg(Arg::new("flag")
