:stderr STDERR -- STDERR is either a buffer or a pipe process attached
to the standard error of subprocess. Specifying this implies
`:connection-type' is set to `pipe'. If STDERR is nil, standard error
-is mixed with standard output and sent to BUFFER or FILTER.
+is mixed with standard output and sent to BUFFER or FILTER. (Note
+that specifying :stderr will create a new, separate (but associated)
+process, with its own filter and sentinel. See
+Info node `(elisp) Asynchronous Processes' for more details.)
:file-handler FILE-HANDLER -- If FILE-HANDLER is non-nil, then look
for a file name handler for the current buffer's `default-directory'