test: cover lowercase compatibility return success

docs/ADVANCED_STATIC_TYPING.md

@@ -355,7 +355,7 @@ Returning text from this method produces a learner-facing diagnostic that names
 Type mismatch for return from Player.score: expected NUMBER, but this value looks like TEXT.
 ```
 
-This is a focused check for simple return expressions. When a parameter has a `CHECK TYPE` declaration, that known type also informs arithmetic return expressions in functions and methods, so `RETURN amount + 1` is checked against the declared return type. A declared return with no `RETURN`, or with a `RETURN` only inside an `IF`, gets a beginner-facing message explaining that the function may finish without returning the promised type:
+This is a focused check for simple return expressions. When a parameter has a `CHECK TYPE` declaration, that known type also informs arithmetic return expressions in functions and methods, so `RETURN amount + 1` is checked against the declared return type. The `RETURNS` keyword is case-insensitive in both modern and compatibility function forms, so `returns NUMBER` keeps working while learners are still getting used to Claro's capitalization. A declared return with no `RETURN`, or with a `RETURN` only inside an `IF`, gets a beginner-facing message explaining that the function may finish without returning the promised type:
 
 ```text
 Function choose declares RETURNS NUMBER but does not return a NUMBER value on every path. Add RETURN to each branch or after the conditional.