Update docs for fallback branch

Author: Bromeon

godot-core/src/classes/match_class.rs

@@ -11,9 +11,12 @@
 /// The current implementation checks [`Gd::try_cast()`][crate::obj::Gd::try_cast] linearly with the number of branches.
 /// This may change in the future.
 ///
-/// Only requires a fallback branch if the type of the expression is different than `()`, and in such case it's required even if all direct known classes are handled. The reason for this is that there may be other subclasses which
-/// are not statically known by godot-rust (e.g. from a script or GDExtension), and the arm needs to return a value of that type. The fallback branch can either be `_` (discard object), or
-/// `variable` to access the original object inside the fallback arm.
+/// When none of the listed classes match, a _fallback branch_ acts as a catch-all and allows to retrieve the original `Gd` pointer.
+/// If the type of the `match_class!` expression is `()`, you can omit the fallback branch. For all other types, it is required, even if all
+/// direct subclasses are handled. The reason for this is that there may be other subclasses which are not statically known by godot-rust
+/// (e.g. from a script or GDExtension).
+///
+/// The fallback branch can either be `_` (discard object), or `variable` to access the original object inside the fallback arm.
 ///
 /// # Example
 /// ```no_run
@@ -51,8 +54,7 @@
 ///     original => 0,
 ///     // Can also be used with mut:
 ///     // mut original => 0,
-///     // It can't be left out because the expression has a type.
-///     // Otherwise, we could've skipped this branch.
+///     // If the match arms have type (), we can also omit the fallback branch.
 /// };
 ///
 /// // event_type is now 0, 1, 2, or 3
@@ -109,7 +111,8 @@ macro_rules! match_class_muncher {
         $block
     }};
 
-    // _ => { ... } or nothing, if there is no need for a return value.
+    // _ => { ... }
+    // or nothing, if fallback is absent and overall expression being ().
     ($subject:ident, $(_ => $block:expr $(,)?)?) => {{
         $($block)?
     }};

itest/rust/src/engine_tests/match_class_test.rs

@@ -136,7 +136,6 @@ fn match_class_named_fallback_unmatched() {
         Resource::new_gd().upcast::<Object>(),
         _node @ Node => 1,
         _res @ Resource => 2,
-        _ignored => 3,
     };
 
     assert_eq!(result, 2);