This format is deprecated and SHOULD NOT BE USED.
It is fairly clear the originator of the format did not intend to accomodate multiple branch libraries, given that the format caps the available namespace to 10,000 barcodes per year TOTAL.
Also, the question of what to do with an item that changes branch is unsettled. Nothing prevents the barcode from working fine, but it will look out of place with the old branchcode in it. Rebarcoding a single item is trivial, but if you consider the scenario of branches being consolidated, it is an unnecessary burden to force the rebarcoding of thousands of items, especially when the format will limit you to under 10,000 on the year!
The main purpose of the format seems to be to get the branch code into the barcode. This is wholly unnecessary, since the barcodes can be printed with the branchcode directly on it, without it being part of the barcode itself.
The API for this module should exist almost exclusively through C4::Barcodes. One novel aspect of this format is the fact that the barcode is tied to a branch.