Remember that "interrogative" means "asking a question." Some questions are perfectly reasonable, and one cannot imagine any problems:

Do you want chocolate, vanilla, or strawberry?

"Chocolate, please."

And then comes the surprise. Users don't wait until the prompt is finished. Instead, they interpret the first part as a "yes-no" question and then immediately barge-in:

Do you want chocolate, ...?

"Yes."

Now we have a problem. It's easy to add "yes" to the grammar. But what does it mean? Is the user saying "yes" to the first flavor, or does the user really want vanilla or strawberry? I have seen this problem completely befuddle designers, who then bend over backwards to avoid the interrogative.

Well of course the key is the timing of the response. If the user misinterprets the interrogative 3-way branch as a yes-no question, then the "yes" will appear between the chocolate and vanilla components of the prompt. VoiceXML supports a feature that allows you to know which prompt sample was playing when barge-in occurred. Applying this feature solves the problem.

Note that it gets a bit more complex if the answer is "no":

Do you want chocolate, ...?

"No."

Great. Now we know what the user doesn't want. But we're stuck with uncertainty between vanilla and strawberry. In this case, the answer is to continue the prompt where it cut off:

Do you want chocolate, ...?

"No."

... vanilla or strawberry?

"Vanilla."

No need to create unique follow-on prompts or to go to a lot of trouble with special explanations. Just carry on. Although these techniques complicate the 3-way branch design, they do so only slightly. If the user interrupts at other points in the prompt—saying, "yes", "no", or even demonstrative OOG such as, "that one"—the solution is easy to design and to code.

I'll leave those special cases as an exercise for the reader.