No meta ibrindex/obrindex, only meta ibrname/obrname

Hello!
I am somewhat new to Linux and am configuring a custom firewall for the 
first time. I have come across a discrepancy wherein the index of an 
interface on a bridge (i.e. a veth bonded to the bridge) cannot be used 
to match in an inet chain, but the name can be used via meta 
ibrname/obrname. I would like to use the index since it is a bit faster 
and my interfaces should not be dynamic, but meta ibrindex/obrindex does 
not exist in any manpages I have read. I checked over the archive as 
best I could and did not see any discussion about the feature either. Is 
this an intentional difference or rather just something which was never 
implemented?
I wish I could offer a fix, but I haven't the faintest idea how a person 
would go about implementing one, so I appreciate any advice on this issue.
Thank you all!