From Facebook Developer Wiki

Can you retrieve the comments for multiple xid's in one call??

Only if you use fql.query on the comment FQL table. You can specify only one XID with this call; I'll clarify that here. Pete (563683308 15:16, 18 June 2009 (PDT))

Is there any way to retrieve a list of XID's used? --574622290 06:28, 22 September 2009 (PDT)

For a specific application you mean, for a given post, or something else? It seems you'd want some context for the comments. Let me know what you're looking for. Thanks, Pete (563683308 17:41, 23 September 2009 (PDT))

[edit] Can you retrieve the last x number of comments from any xid?

It looks like you have to specify each xid, but how would you retrieve the last 10 comments for any xid? It's hard to get a conversation going when visitors can't see what comments have been made among hundreds of pages.

[edit] xid vs. object_id

The documentation indicates that I can say 'get("", <object_id>, ...)' where <object_id> refers to a photo. But, making such a call returns an empty list.

I went to [1] for help, but comments.get only lists the xid parameter there.

What gives?

Thanks!

Never mind. I was using 'pid', rather than 'object_id'.