BIOs can be joined together to form a chain (a single BIO is a chain
with one component). A chain normally consist of one source/sink
BIO and one or more filter BIOs. Data read from or written to the
-end BIO then traverses the chain to the end (normally a source/sink
+first BIO then traverses the chain to the end (normally a source/sink
BIO).
=head1 SEE ALSO