There were a few people who asked in the last few months if it was possible to determine which Friend's page was being viewed. That is, the ability to determine if it was the regular friends page (/friends), or a filter page (/friends/filter) or the friends' friends page (/friendsfriends). At that time, it was not possible.
Due to updates that were made in the last few days to the S2 core, it is now possible. On the FriendsPage class, there are three new variables:
filter_active - A bool variable. The value is True if a filter is being used, False otherwise.
filter_name - A string variable. The value is the name of the filter if one is being used, empty otherwise.
friends_mode - A string variable. The value is "friendsfriends" if viewing the Friends' Friends page, empty otherwise.
They've also modified the core to adjust the output of the view_title() function on the friends pages to reflect this new information that's available and it's been automatically incorporated into Component. I thought I'd let everybody know just in case you could find some interesting use for it.