@asiekierka
I would have reported this on the stackup issue tracker but account registration seems to disabled.
In this blogpost you suggested id="minecraft:apple" = 256 but this doesn't actually appear to be valid syntax. I am getting exceptions with this: https://pastebin.com/raw/2c3ctJPN
Could you adjust the documentation to match the code?
Thanks for coding the mod!

[14:32:56] [main/INFO] [STDERR]: [pl.asie.stackup.script.ScriptContext:execute:66]: pl.asie.stackup.script.TokenException: Token not found: !

Where's the ! ?

Is a ! required? The documentation does not seem to mention it.
id="minecraft:apple" = 32 Throws the exception
id="minecraft:apple" -> 32 works fine
I'm guessing this is mostly just the blog post being outdated.
Versions: Stackup 0.2.3 on Forge 2768, minecraft 1.12.2