Document question about bond-swap

Dear Lammps users,

I just read the document about the fix bond/swap.
IMPORTANT NOTE: If your simulation uses molecule IDs in the usual way, where all monomers
on a single chain are assigned the same ID (different for each chain), then swaps will only occur
within the same chain and will NOT conserve chain length. This is probably not what you want for
this fix.

I donot understant why the chain length could not be conserved.
I think the chain length should be conserved since the swaps only occur within the same chain.
That means no bead would be lost.
Am I right?
Thank you and looking forward to explanation.

Best wishes,

Zhiwei Cui

What it means is the 2 chain "ends" that are swapped
do not conserve their respective lengths. This is b/c
the swap can occur in principle between any pair
of bonds within the chain. Whether that is good
or bad is up to you ...