Where is the message instance property of MFMessageComposeViewController?

Why am I not seeing the message instance property of MFMessageComposeViewController? When I type the following, I get a code-time error message in Xcode that says "Value of type 'MFMessageComposeViewController' has no member 'message'"

messageComposeViewController.message // error message: "Value of type 'MFMessageComposeViewController' has no member 'message'"

There is nothing that explains this in the official Apple documentation: Documentation/Message UI/MFMessageComposeViewController/message

Where is the message instance property of MFMessageComposeViewController?
 
 
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