+=item B<$of>->seekable
+
+Returns whether or not the data source being read is seekable.
+
+=item B<$of>->link_count
+
+Returns the number of links in this chained stream. Always returns 1
+for unseekable sources.
+
+=item B<$of>->serialno([I<$link_index>])
+
+Get the serial number of the given link in a (possibly-chained) Ogg
+Opus stream. If the given index is greater than the total number of
+links, this returns the serial number of the last link.
+
+If the source is not seekable, I<$link_index> is negative, or
+I<$link_index> is not given, then this function returns the serial
+number of the current link.
+