found a piece not mentioned in tutorials

I found a piece in my iPhone 5S that I can't find in tutorials :

https://dl.dropboxusercontent.com/u/2994...

It was near this area :

https://dl.dropboxusercontent.com/u/2994...

I guess it was near this connector (circled in green), but don't know in which way with motherboard or other elements. This iPhone was bought 7 month after the launch of 5S.

Any help ?

thx !

is it ? : back from iPhone, then unknown piece, then motherboard, then connector piece screwed on the side then screw to fix the whole things ? I'm stil wondering orientation and which side although. Can you find any picture on the net to help ?