+ /** Perform one decode pass of the content, which may or may not
+ * result in a complete quantum (Decoded object) of decoded stuff
+ * being added to _pending.
+ * @return true if the decoder is done (i.e. no more data will be
+ * produced by any future calls to pass() without a seek() first).
+ */
+ virtual bool pass () = 0;
+ virtual void flush () {};
+