+ /**
+ * Set up an output channel. String or byte data can be added without problem.
+ *
+ * @param bytePoster a byte poster can take the output byte[] when closing and
+ * do something with them
+ * @param fileName TODO: It is possible that JavaScript will call this with a
+ * function name for fileName
+ * @param asWriter string-based
+ * @param os the desired target OutputStream - not the calling stream!
+ * @return
+ */