Clarify delegate targetting function-level block

proposals/exception-handling/Exceptions.md

@@ -288,8 +288,7 @@ end
 If `call $foo` throws, searching for a catching block first finds `delegate`,
 and because it delegates exception handling to catching instructions associated
 with `$l1`, it will be next checked by the outer `catch` and then `catch_all`
-instructions. When the specified label within a `delegate` instruction does not
-correspond to a `try` instruction, it is a validation failure.
+instructions.
 
 Note that the example below is a validation failure:
 ```
@@ -311,6 +310,41 @@ catching instructions (`catch`/`catch_all`/`delegate`) come after the
 same as if the `try` has catches but none of the catches are able to handle the
 exception.
 
+If `delegate`'s immediate argument is the depth of the outermost block + 1, i.e.
+the function-level block, the function-level block is considered as a
+`catch`-less `try` and it delegates the exception handling to the caller of the
+current function. For example:
+```
+(func $test
+  try $l1
+    try
+      call $foo
+    delegate 1  ;; delegate to the caller
+  catch
+    ...
+  catch_all
+    ...
+  end
+)
+```
+In case `foo` throws, `delegate 1` here delegates the exception handling to the
+caller, i.e., the exception escapes the current function.
+
+When the specified label within a `delegate` instruction does not correspond to
+a `try` instruction or the function-level, it is a validation failure:
+```
+block $l0
+  loop $l1
+    try
+      call $foo
+    delegate $l0  ;; targets a 'block', validation failure
+    try
+      call $foo
+    delegate $l1  ;; targets a 'loop', validation failure
+  end
+end
+```
+
 ### JS API
 
 #### Stack traces