I am using API 28 but when I try to use sforce.interaction.searchAndGetScreenPopURL from my viusalforce page I get an error indicating the object has no such method. Why would that be? is it not in API 28?

<script src="/support/api/28.0/interaction.js"></script>

I am using API 28 but when I try to use sforce.interaction.searchAndGetScreenPopURL from my viusalforce page I get an error indicating the object has no such method. Why would that be? is it not in API 28?

<script src="/support/api/28.0/interaction.js"></script>