[Koha-devel] what is a 'PE' branch ?

Hello, could someone explain to me what is the meaning (functionnaly speaking) of this portion of code : (C4/Circulation.pm) # check if the book is in a permanent collection.... my $hbr = $iteminformation->{'homebranch'}; my $branches = GetBranches(); if ( $hbr && $branches->{$hbr}->{'PE'} ) { $messages->{'IsPermanent'} = $hbr; }