Zero - cannot open the file, nonzero - file opened.
Value of the parameter is used later when calling other %FIO_*
functions, which need it. Value is valid within the ESL script instance, the function was called from.
Having finished work with the file, it must be
closed by calling the function %FIO_Close.
If execution of ESL script is terminated early, the
process D2000 EventHandler
will automatically close all open files.