The automatic tests passed, so there can't really be any syntactical errors in the code.
It might look confusing at first, but in Rust, putting the condition in () is not necessary - discouraged, even -, while the {} around each arm is mandatory. Almost opposite of how it is in C.
And I'm not exactly sure how this would relate to type safety anyways.

Thank you for the reply. This helps clarify it for me. I was originally wondering how it passed the test with the syntax. Now I know why. I am just so used to the strict syntax in Python when it comes to whitespace and parentheses and most other programming languages requiring a paranthese to always have a closing paranthese. example:

foo = str(input("Sample")) # Correct
bar = str(input("Sample") # Incorrect

Also, I used the word type safety, as I mistook it for a type of syntax error. I will try to get a better definition of type safety and just say "possible syntax error" from now on.

I don't believe you should use the prototypes to check for XML/XMLList, here's a test:
XMLproto.zip
Outputs "xml" twice in Ruffle, "object" and then "xml" in Flash Player.

Thank you!