Answer a FileStream that is attached the Smalltalk program's standard
error file handle, which can be used for error messages and diagnostics
issued by the program.
stdin
Answer a FileStream that is attached the Smalltalk program's standard
input file handle, which is the normal source of input for the program.
stdout
Answer a FileStream that is attached the Smalltalk program's standard
output file handle; this is used for normal output from the program.