The tracking issue for this feature is: #43781

The doc_cfg feature allows an API be documented as only available in some specific platforms. This attribute has two effects:

1. In the annotated item's documentation, there will be a message saying "This is supported on (platform) only".

2. The item's doc-tests will only run on the specific platform.

In addition to allowing the use of the #[doc(cfg)] attribute, this feature enables the use of a special conditional compilation flag, #[cfg(rustdoc)], set whenever building documentation on your crate.

This feature was introduced as part of PR #43348 to allow the platform-specific parts of the standard library be documented.

# #![allow(unused_variables)]
#![feature(doc_cfg)]

#fn main() {
#[cfg(any(windows, rustdoc))]
#[doc(cfg(windows))]
/// The application's icon in the notification area (a.k.a. system tray).
///
/// # Examples
///
/// ```no_run
/// extern crate my_awesome_ui_library;
/// use my_awesome_ui_library::current_app;
/// use my_awesome_ui_library::windows::notification;
///
/// let icon = current_app().get::<notification::Icon>();
/// icon.show();
/// icon.show_message("Hello");
/// ```
pub struct Icon {
    // ...
}
#}