Why add letter “f” before a numeric ?

Hi,

i’m wondering why Buddydrive add the letter “F” before a numeric ?
Here :
https://github.com/imath/buddydrive/blob/master/includes/buddydrive-item-functions.php#L621-L623

The users of my client need to add numeric folder to classify correctly their documents.
I give the follow trick : after adding your numeric folder, modify it removing “f-“. It works.

But this trick is tedious.
So for now, i use “buddydrive_item_before_save” action to rewrite “f-XXX” to “XXX”.
But if, one day, a user really want “f-xxx” title, it still will be rewritten.

Thanks in advance for your anwser,

JL