Thanks, I also posted it there. Actually, it took spending time on the JavaScript sites to eventually figure out the answer. Here is what works for me:
On the change event:
//Test input in real time. Only allow approved grades between 1 and 100, r, i, n
if (xfa.this.change!="" && !xfa.event.newText.match(/^[1-9][0-9]?$|^100|^(n|r|i)$/)){
xfa.event.change ="";
xfa.host.messageBox("Incorrect entry... Thanks!");
}