+ /**
+ * Flush the {@link BufferedOutputStream}, write the current buffered data
+ * to (and optionally also flush) the under-laying stream.
+ * <p>
+ * If {@link BufferedOutputStream#bypassFlush} is false, all writes to the
+ * under-laying stream are done in this method.
+ * <p>
+ * This can be used if you want to write some data in the under-laying
+ * stream yourself (in that case, flush this {@link BufferedOutputStream}
+ * with or without flushing the under-laying stream, then you can write to
+ * the under-laying stream).
+ * <p>
+ * <b>But be careful!</b> If a replacement could be done with the end o the
+ * currently buffered data and the start of the data to come, we obviously
+ * will not be able to do it.
+ *
+ * @param includingSubStream
+ * also flush the under-laying stream
+ * @throws IOException
+ * in case of I/O error
+ */