Fb:switch
From Facebook Developer Wiki
Description
Evaluates every fb: tag inside and returns the first one that evaluates to anything other than an empty string. You can use fb:default to specify a default that gets rendered if nothing else does before it was executed.
Examples
<fb:switch>
<fb:photo pid="12345" />
<fb:profile-pic uid="54321" />
<fb:default>You can't see either the photo or the profile pic</fb:default>
</fb:switch>
Note: fb:default always returns its content. Thus, if it is the first tag within fb:switch, then no other tags get tested.
