gre.APP_ROOT
This is a variable that is filled in by the Storyboard Engine to point at the filesystem path for the application's project root directory. This can be used in order to access resources in a project relative manner. This variable is only applicable for filesystem based configurations.
Historical code may use gre.SCRIPT_ROOT .. "/.." as a way of referring to files in a project
relative manner, but gre.APP_ROOT is preferred as not all filesystems support relative path operations.
Unix forward slash directory path separator conventions are preferred when working file filenames.
Example:
-- Open the french translation file in the translations folder
local translation_file = gre.APP_ROOT .. "/translations/french.csv"
local fp = io.open(translation_file, "r")
...