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diff --git a/doc/man3/BIO_f_readbuffer.pod b/doc/man3/BIO_f_readbuffer.pod
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+=pod
+
+=head1 NAME
+
+BIO_f_readbuffer
+- read only buffering BIO that supports BIO_tell() and BIO_seek()
+
+=head1 SYNOPSIS
+
+ #include <openssl/bio.h>
+
+ const BIO_METHOD *BIO_f_readbuffer(void);
+
+=head1 DESCRIPTION
+
+BIO_f_readbuffer() returns the read buffering BIO method.
+
+This BIO filter can be inserted on top of BIO's that do not support BIO_tell()
+or BIO_seek() (e.g. A file BIO that uses stdin).
+
+Data read from a read buffering BIO comes from an internal buffer which is
+filled from the next BIO in the chain.
+
+BIO_gets() is supported for read buffering BIOs.
+Writing data to a read buffering BIO is not supported.
+
+Calling BIO_reset() on a read buffering BIO does not clear any buffered data.
+
+=head1 NOTES
+
+Read buffering BIOs implement BIO_read_ex() by using BIO_read_ex() operations
+on the next BIO (e.g. a file BIO) in the chain and storing the result in an
+internal buffer, from which bytes are given back to the caller as appropriate
+for the call. BIO_read_ex() is guaranteed to give the caller the number of bytes
+it asks for, unless there's an error or end of communication is reached in the
+next BIO. The internal buffer can grow to cache the entire contents of the next
+BIO in the chain. BIO_seek() uses the internal buffer, so that it can only seek
+into data that is already read.
+
+=head1 RETURN VALUES
+
+BIO_f_readbuffer() returns the read buffering BIO method.
+
+=head1 SEE ALSO
+
+L<bio(7)>,
+L<BIO_read(3)>,
+L<BIO_gets(3)>,
+L<BIO_reset(3)>,
+L<BIO_ctrl(3)>.
+
+=head1 COPYRIGHT
+
+Copyright 2021 The OpenSSL Project Authors. All Rights Reserved.
+
+Licensed under the Apache License 2.0 (the "License").  You may not use
+this file except in compliance with the License.  You can obtain a copy
+in the file LICENSE in the source distribution or at
+L<https://www.openssl.org/source/license.html>.
+
+=cut