Assertion and EncryptedAssertion

Dear SAML experts,
I have a question regarding Assertion and EncryptedAssertion.
I think I need either Assertion or EncryptedAssertion in the SAMLResponse but not both for it to work.
Correct me if I am wrong.

However, I did not see in the document that a response can only have exactly one Assertion or EncryptedAssertion.
Is it defined in the schema?

Thank you so much again
David