The loader preprocessor will set the script’s loader.
You call the loader Preprocessor by adding
#loader loaderName to your script file with
loaderName being the name of the loader you want to assign the script to.
What it does
Scripts with the loader Preprocessor will only be loaded by the loader specified.
In the example above, crafttweaker’s loader won’t touch the file, instead the loader called “contentTweaker” will execute that script.
If you don’t specify that preprocessor, it will default to being “crafttweaker”.