Is user authorized, on Facebook tab

Getting an interesting error. I've been developing and application, and viewing it on it's page. Now I'm install that app in as tab on a company page and it's sayi开发者_JAVA技巧ng I can't use:

<fb:if-is-app-user>

in the tab view? How can I show or hide part of the page if the user viewing it is an app user?

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FBML fan page tabs have been deprecated and replaced with Facebook iframe pages. To determine if the user is fan, you will need to decode the signed_request parameter that gets POST'ed to your webpage. There will be a "liked" variable in the encoded json payload. This page gives an example of how the new process works,