How to determine type of nftables set

I am working on an application that will be working with pre-existing
(created by the system administrator) netfilter sets.  These sets should
contain either IPv4 of IPv6 addresses.

How can my application determine what type of address a particular set
holds?  I can query the set and get a NFT_MSG_GETSET message back, but
it's murky after that.

The message contains a NFTA_SET_KEY_TYPE attribute, which looks
promising, but I can't find anything telling me how to interpret it.
ChatGPT says that I should just look at the NFTA_SET_KEY_LEN attribute,
but that doesn't seem reliable; how would I distinguish a 32-bit IPv4
address from 2 16-bit ports?

Short of digging through the source code of nft, how am I supposed to do
this?

TIA!

-- 
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If your user interface is intuitive in retrospect ... it isn't intuitive
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