You can add anything you want as long as you don't use more than 100 semicolons. Basically, you can't hide functions, etc into another file - that wouldn't be fair. If you need another file use it, but make sure that the total number of semicolons stays below 101.
What do you mean by this? That it wouldn't be fair for example to write a fx file converted to ascii code numbers into the rgb channels of a picture and deconvert it in the project using some simpel pixel_for_bmap and str_for_asc instructions??
