diff --git a/Doc/library/pty.rst b/Doc/library/pty.rst
index 0ab7660..1226843 100644
--- a/Doc/library/pty.rst
+++ b/Doc/library/pty.rst
@@ -43,11 +43,32 @@
 
    Spawn a process, and connect its controlling terminal with the current
    process's standard io. This is often used to baffle programs which insist on
-   reading from the controlling terminal.
+   reading from the controlling terminal. It is expected that the process
+   spawned behind the pty will eventually terminate, and when it does *spawn*
+   will return.
 
-   The functions *master_read* and *stdin_read* should be functions which read from
-   a file descriptor. The defaults try to read 1024 bytes each time they are
-   called.
+   The functions *master_read* and *stdin_read* are passed a file descriptor
+   which they should read from, and they should always return a byte string. In
+   order to force spawn to return before the child process exits an
+   :exc:`OSError` should be thrown.
+
+   The default implementation for both functions will read and return up to 1024
+   bytes each time the function is called. The *master_read* callback is passed
+   the pseudoterminal’s master file descriptor to read output from the child
+   process, and *stdin_read* is passed file descriptor 0, to read from the
+   parent process's standard input.
+
+   Returning an empty byte string from either callback is interpreted as an
+   end-of-file (EOF) condition, and that callback will not be called after
+   that. If *stdin_read* signals EOF the controlling terminal can no longer
+   communicate with the parent process OR the child process. Unless the child
+   process will quit without any input, *spawn* will then loop forever. If
+   *master_read* signals EOF the same behavior results (on linux at least).
+
+   If both callbacks signal EOF then *spawn* will probably never return, unless
+   *select* throws an error on your platform when passed three empty lists. This
+   is a bug, documented in `issue 26228 <https://bugs.python.org/issue26228>`_.
+
 
    .. versionchanged:: 3.4
       :func:`spawn` now returns the status value from :func:`os.waitpid`
diff --git a/Misc/ACKS b/Misc/ACKS
index 77f1990..f9d01d0 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1859,3 +1859,4 @@
 Carsten Klein
 Diego Rojas
 Edison Abahurire
+Geoff Shannon
diff --git a/Misc/NEWS.d/next/Documentation/2019-02-21-18-13-50.bpo-22865.6hg6J8.rst b/Misc/NEWS.d/next/Documentation/2019-02-21-18-13-50.bpo-22865.6hg6J8.rst
new file mode 100644
index 0000000..67a4ed2
--- /dev/null
+++ b/Misc/NEWS.d/next/Documentation/2019-02-21-18-13-50.bpo-22865.6hg6J8.rst
@@ -0,0 +1 @@
+Add detail to the documentation on the `pty.spawn` function.
\ No newline at end of file