+ * 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).