HyperCard's Answer command produces a dialog box with up to three buttons,
where the rightmost button is the default.
To specify which of the buttons is to be the default button, make it the
last definition in the list. (There is no way to avoid having a default
button.)
At this point, we know of no XCMDs or XFCNs that customize the dialog box
to include more text or buttons. It would be much easier to trap the
"answer" message and have it execute an XFCN instead.