Hi Harry,
Based on your sample answer syntax it looks like you are trying to use a Cloze type question. If that's correct, use the example Emma provided.
If you do want to use a gap fill question then the answer syntax would be:
Question: Who is the Gotham Protector?
Answer: [Batman|Dark Knight|batman|dark knight]
When editing the question, under More Options > Show more, if you remove the checkmark for Case Sensitive, then you could use this:Question: Who is the Gotham Protector?
Answer: [batman|dark knight]