diff --git a/h/arch.h b/h/arch.h
index 9d6e99cd8..fc003de41 100644
--- a/h/arch.h
+++ b/h/arch.h
@@ -9,9 +9,12 @@
 
 #define	ARMAG	0177545
 #define AALMAG	0177454
+#define AR_NAME_MAX 14
 
 struct	ar_hdr {
-	char	ar_name[14];
+	/** null terminated filename. */
+	char	ar_name[AR_NAME_MAX];
+	/** last modification time, defined as seconds since epoch. */
 	long	ar_date;
 	char	ar_uid;
 	char	ar_gid;
@@ -22,4 +25,33 @@ struct	ar_hdr {
 #define AR_TOTAL	26
 #define AR_SIZE		22
 
+
+/** ar_mode Read permission bit for the owner of the file. */
+#define AR_IRUSR	0400
+/** ar_mode Write permission bit for the owner of the file. */
+#define AR_IWUSR	0200
+/** ar_mode Execute (for ordinary files) or search (for directories)
+ *  permission bit for the owner of the file.
+ */
+#define AR_IXUSR	0100
+/** ar_mode Read permission bit for the group owner of the file. */
+#define AR_IRGRP	040
+/** ar_mode Write permission bit for the group owner of the file. */
+#define AR_IWGRP	020
+/** ar_mode Execute or search permission bit for the group owner of the file. */
+#define AR_IXGRP	010
+/** ar_mode Read permission bit for other users. */
+#define AR_IROTH	04
+/** ar_mode Write permission for other users. */
+#define AR_IWOTH	02
+/** ar_mode Execute or search permission bit for other users. */
+#define AR_IXOTH	01
+
+/* This is the set-user-ID on execute bit. */
+#define	AR_ISUID	04000
+/* This is the set-group-ID on execute bit. */
+#define	AR_ISGID	02000
+
+
+
 #endif /* __ARCH_H_INCLUDED */