-#ifdef OPENSSL_SYS_MSDOS
-# define OPENSSL_UNISTD_IO <io.h>
-# define OPENSSL_DECLARE_EXIT extern void exit(int);
-#else
-# define OPENSSL_UNISTD_IO OPENSSL_UNISTD
-# define OPENSSL_DECLARE_EXIT /* declared in unistd.h */
-#endif
+# ifdef OPENSSL_SYS_MSDOS
+# define OPENSSL_UNISTD_IO <io.h>
+# define OPENSSL_DECLARE_EXIT extern void exit(int);
+# else
+# define OPENSSL_UNISTD_IO OPENSSL_UNISTD
+# define OPENSSL_DECLARE_EXIT /* declared in unistd.h */
+# endif
+
+/*-
+ * Definitions of OPENSSL_GLOBAL and OPENSSL_EXTERN, to define and declare
+ * certain global symbols that, with some compilers under VMS, have to be
+ * defined and declared explicitely with globaldef and globalref.
+ * Definitions of OPENSSL_EXPORT and OPENSSL_IMPORT, to define and declare
+ * DLL exports and imports for compilers under Win32. These are a little
+ * more complicated to use. Basically, for any library that exports some
+ * global variables, the following code must be present in the header file
+ * that declares them, before OPENSSL_EXTERN is used:
+ *
+ * #ifdef SOME_BUILD_FLAG_MACRO
+ * # undef OPENSSL_EXTERN
+ * # define OPENSSL_EXTERN OPENSSL_EXPORT
+ * #endif
+ *
+ * The default is to have OPENSSL_EXPORT, OPENSSL_IMPORT and OPENSSL_GLOBAL
+ * have some generally sensible values, and for OPENSSL_EXTERN to have the
+ * value OPENSSL_IMPORT.
+ */