How does bash coprocess achieve its pipelining?

Note this passage from man bash ( emphasis mine ): > Coprocesses > > A coprocess is a shell command preceded by the coproc reserved word. A > coprocess is executed asynchronously in a subshell, as if the command > had been terminated with the & control operator, **with a two-way pipe** > established between the executing shell and the coprocess. Now, as we know unlike other *nix systems, Linux pipes are unidirectional (also ref man pipe(7) , Portability section). So how does bash coproces achieve the "two-way pipe" without one existing on Linux ?