id is an arbitrary string assigned by the user. id must be unique per pcb-rnd session per script and may contain alphanumeric characters and undescrore.

fn is the file name of the script, which is a path. Pcb-rnd does not do any search, it only opens the path as specified.

lang is the scripting language, as in fungw plugin name. When not specified, the code makes a guess (based on the file name).