Frealign using data from different collections

Hi Niko, hi everybody!

I read that frealign supports multiple datasets from different collections. How do I use this feature? My datasets have small differences in respect to pix_size and some fluctuation regarding the Voltage between the collections.
I tried simply providing two stacks and .par-files and giving two "# Dataset-specific parameters"-blocks in the mparameters file. When I do this i get: "if: Expression Syntax."

Thanks for the help!

Lukas