desktop/token: Show backend feature requirement

src/desktop/handle_token.rs

@@ -9,8 +9,9 @@ use serde::{Deserialize, Serialize};
 use zbus::zvariant::OwnedObjectPath;
 use zbus::{names::OwnedMemberName, zvariant::Type};
 
-/// A handle token is a DBus Object Path element, specified in the
-/// [`Request`](crate::desktop::Request)  or
+/// A handle token is a DBus Object Path element.
+///
+/// Specified in the [`Request`](crate::desktop::Request)  or
 /// [`Session`](crate::desktop::Session) object path following this format
 /// `/org/freedesktop/portal/desktop/request/SENDER/TOKEN` where sender is the
 /// caller's unique name and token is the [`HandleToken`].

src/desktop/mod.rs

@@ -1,6 +1,7 @@
 mod handle_token;
 pub(crate) mod request;
 mod session;
+#[cfg_attr(docsrs, doc(cfg(feature = "backend")))]
 #[cfg(feature = "backend")]
 pub use self::handle_token::HandleToken;
 #[cfg(not(feature = "backend"))]