Dynamically appending addresses to a named set

Hello,

In NFTables, I have created a named set called 'bar' in the chain input
in the table foo.  I can add elements to the set manually,

# nft add element ip foo bar { 192.168.2.2 }

However, I am not able to guess the syntax to have a regular NFTables
rule do the appending automatically.  I've tried a lot of permutations
of the following, but always with fatal errors,

# nft add rule foo input tcp dport 22 counter add @bar { ip saddr }
Error: Could not process rule: Operation not supported
add rule foo input tcp dport 22 counter add @bar { ip saddr }

# nft add rule foo input tcp dport 22 add element @bar { ip saddr }
Error: syntax error, unexpected element, expecting @ or '$'
add rule foo input tcp dport 22 add element @bar { ip saddr }

What would be the correct syntax to have a rule which automatically adds
a source IP address to the named set when certain conditions are met?

/Lars