Github user cestella commented on the issue:
https://github.com/apache/metron/pull/687
@nickwallen No, that's not correct. Stellar enrichments can contain `:=`.
Consider the enrichments
[here](https://github.com/apache/metron/tree/master/use-cases/geographic_login_outliers#enrich-authentication-events)
in one of our use-cases. Enrichments can either take a map of enrichments or
a list of strings. If you pass a list of strings (which you would need to do
to create temporary variables that you then remove before passing through, like
in the example), you'd use an assignment, which is currently `:=`.
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