-extern int wxAddProcessCallback(wxEndProcessData *proc_data, int fd);
-
-#if defined(__DARWIN__) && (defined(__WXMAC__) || defined(__WXCOCOA__))
+//
+// The file descriptor 'fd' is descriptor of a dummy pipe opened between the
+// parent and the child. No data are written to or read from this pipe, its
+// sole purpose is that the child process will close it when it terminates and
+// the parent will be notified about it if it looks at 'fd' (e.g. using
+// select()).
+//
+// wxAddProcessCallback() does whatever is necessary to ensure that 'fd' is
+// periodically (typically every event loop iteration) checked for its status
+// and that wxHandleProcessTermination() is called once 'fd' indicates the
+// child terminated.
+extern WXDLLIMPEXP_CORE int wxAddProcessCallback(wxEndProcessData *proc_data, int fd);
+
+#if defined(__WXMAC__) || defined(__WXCOCOA__)