Placeholder value modifier expand not recognized

[r0ot]

The sigma language supports a value modifier called expand that allows dynamic, environment-specific values to be populated through a translation pipeline. See the blog.sigmahq.io writeup here.

When a sigma rule with this logic is attempted to be translated by uncoder the following error message is received:
Unexpected error. Unexpected token type: expand.
(Example sigma rule file: https://github.com/SigmaHQ/sigma/blob/master/rules-placeholder/cloud/azure/azure_ad_account_created_deleted_nonapproved_user.yml)

It doesn't seem to matter what output format uncoder is instructed.

Does uncoder currently support this and I'm just doing it wrong?
If so, is there documentation for it that I can't find?
If not, are there plans to implement it?