+@node Bivalent Streams
+@section Bivalent Streams
+
+A @dfn{bivalent stream} can be used to read and write both
+@code{character} and @code{(unsigned-byte 8)} values. A bivalent
+stream is created by calling @code{open} with the argument @code{:element-type
+:default}. On such a stream, both binary and character data can be
+read and written with the usual input and output functions.
+
+@c Horrible visual markup
+@quotation
+Streams are @emph{not} created bivalent by default for performance
+reasons. Bivalent streams are incompatible with
+@code{fast-read-char}, an internal optimization in sbcl's stream
+machinery that bulk-converts octets to characters and implements a
+fast path through @code{read-char}.
+@end quotation
+