@@ -81,8 +81,10 @@ underlying :class:`Popen` interface can be used directly.
8181
8282 If *env * is not ``None ``, it must be a mapping that defines the environment
8383 variables for the new process; these are used instead of the default
84- behavior of inheriting the current process' environment. It is passed directly
85- to:class: `Popen `.
84+ behavior of inheriting the current process' environment. It is passed
85+ directly to:class: `Popen `. This mapping can be str to str on any platform
86+ or bytes to bytes on POSIX platforms much like:data: `os.environ ` or
87+ :data: `os.environb `.
8688
8789 Examples::
8890
@@ -619,7 +621,9 @@ functions.
619621
620622 If *env * is not ``None ``, it must be a mapping that defines the environment
621623 variables for the new process; these are used instead of the default
622- behavior of inheriting the current process' environment.
624+ behavior of inheriting the current process' environment. This mapping can be
625+ str to str on any platform or bytes to bytes on POSIX platforms much like
626+ :data: `os.environ ` or:data: `os.environb `.
623627
624628 ..note ::
625629