How do I derive variables from Placeholders?

[san4d]

What's the idiomatic way to represent derived variables? For example, I want to save the result of {{ val | downcase }} to a variable so I don't have to repeat the definition in multiple locations, where val was defined in a placeholder block.

I checked a few projects with the cargo-generate topic, but I couldn't find an example.

My thought was to set the variables during the Pre hook stage with a Rhai script.

[sassman]

according to the liquid docs it should work this way:

{% assign my_variable = false %}

But I've never tried it myself.