LittleFoot: from metadata to compiled program

I am trying to upload LittleFoot programs from an application I am developing. Some of the programs use metadata and obviously this prevent the program to compile as is.
Unfortunately, It is difficult to find any documentation on metadata.

Here my question:

Are metadata variables inside the Littlefoot program just placeholders replaced by actual values before the program is compiled? Or is there some kind of metadata to heap transformation happening as part of a compile process?