From: nicm <nicm@openbsd.org>
Date: Wed, 21 Aug 2024 04:17:09 +0000 (+0000)
Subject: Revamp extended keys support to more closely match xterm and support
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=719f5715a68555953a1997f39792665cc714f31c;p=openbsd

Revamp extended keys support to more closely match xterm and support
mode 2 as well as mode 1. From Stanislav Kljuhhin (GitHub issue 4038).

This changes tmux to always request mode 2 from parent terminal, change
to an unambiguous internal representation of keys, and adds an option
(extended-keys-format) to control the format similar to the xterm(1)
formatOtherKeys resource.
---

diff --git a/usr.bin/tmux/format.c b/usr.bin/tmux/format.c
index 2377697bcba..aa17e924ffe 100644
--- a/usr.bin/tmux/format.c
+++ b/usr.bin/tmux/format.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: format.c,v 1.318 2023/09/08 06:52:31 nicm Exp $ */
+/* $OpenBSD: format.c,v 1.319 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2011 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1962,6 +1962,23 @@ format_cb_pane_unseen_changes(struct format_tree *ft)
 	return (NULL);
 }
 
+/* Callback for pane_key_mode. */
+static void *
+format_cb_pane_key_mode(struct format_tree *ft)
+{
+	if (ft->wp != NULL && ft->wp->screen != NULL) {
+		switch (ft->wp->screen->mode & EXTENDED_KEY_MODES) {
+		case MODE_KEYS_EXTENDED:
+			return (xstrdup("Ext 1"));
+		case MODE_KEYS_EXTENDED_2:
+			return (xstrdup("Ext 2"));
+		default:
+			return (xstrdup("VT10x"));
+		}
+	}
+	return (NULL);
+}
+
 /* Callback for pane_last. */
 static void *
 format_cb_pane_last(struct format_tree *ft)
@@ -2997,6 +3014,9 @@ static const struct format_table_entry format_table[] = {
 	{ "pane_input_off", FORMAT_TABLE_STRING,
 	  format_cb_pane_input_off
 	},
+	{ "pane_key_mode", FORMAT_TABLE_STRING,
+	  format_cb_pane_key_mode
+	},
 	{ "pane_last", FORMAT_TABLE_STRING,
 	  format_cb_pane_last
 	},
diff --git a/usr.bin/tmux/input-keys.c b/usr.bin/tmux/input-keys.c
index 3dbf465eca9..7a83b165e48 100644
--- a/usr.bin/tmux/input-keys.c
+++ b/usr.bin/tmux/input-keys.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: input-keys.c,v 1.94 2023/01/12 18:49:11 nicm Exp $ */
+/* $OpenBSD: input-keys.c,v 1.95 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -308,20 +308,6 @@ static struct input_key_entry input_key_defaults[] = {
 	{ .key = KEYC_DC|KEYC_BUILD_MODIFIERS,
 	  .data = "\033[3;_~"
 	},
-
-	/* Tab and modifiers. */
-	{ .key = '\011'|KEYC_CTRL,
-	  .data = "\011"
-	},
-	{ .key = '\011'|KEYC_CTRL|KEYC_EXTENDED,
-	  .data = "\033[9;5u"
-	},
-	{ .key = '\011'|KEYC_CTRL|KEYC_SHIFT,
-	  .data = "\033[Z"
-	},
-	{ .key = '\011'|KEYC_CTRL|KEYC_SHIFT|KEYC_EXTENDED,
-	  .data = "\033[1;5Z"
-	}
 };
 static const key_code input_key_modifiers[] = {
 	0,
@@ -427,14 +413,163 @@ input_key_write(const char *from, struct bufferevent *bev, const char *data,
 	bufferevent_write(bev, data, size);
 }
 
+/*
+ * Encode and write an extended key escape sequence in one of the two
+ * possible formats, depending on the configured output mode.
+ */
+static int
+input_key_extended(struct bufferevent *bev, key_code key)
+{
+	char		 tmp[64], modifier;
+	struct utf8_data ud;
+	wchar_t		 wc;
+
+	switch (key & KEYC_MASK_MODIFIERS) {
+	case KEYC_SHIFT:
+		modifier = '2';
+		break;
+	case KEYC_META:
+		modifier = '3';
+		break;
+	case KEYC_SHIFT|KEYC_META:
+		modifier = '4';
+		break;
+	case KEYC_CTRL:
+		modifier = '5';
+		break;
+	case KEYC_SHIFT|KEYC_CTRL:
+		modifier = '6';
+		break;
+	case KEYC_META|KEYC_CTRL:
+		modifier = '7';
+		break;
+	case KEYC_SHIFT|KEYC_META|KEYC_CTRL:
+		modifier = '8';
+		break;
+	default:
+		return (-1);
+	}
+
+	if (KEYC_IS_UNICODE(key)) {
+		utf8_to_data(key & KEYC_MASK_KEY, &ud);
+		if (utf8_towc(&ud, &wc) == UTF8_DONE)
+			key = wc;
+		else
+			return (-1);
+	} else
+		key &= KEYC_MASK_KEY;
+
+	if (options_get_number(global_options, "extended-keys-format") == 1)
+		xsnprintf(tmp, sizeof tmp, "\033[27;%c;%llu~", modifier, key);
+	else
+		xsnprintf(tmp, sizeof tmp, "\033[%llu;%cu", key, modifier);
+
+	input_key_write(__func__, bev, tmp, strlen(tmp));
+	return (0);
+}
+
+/*
+ * Outputs the key in the "standard" mode. This is by far the most
+ * complicated output mode, with a lot of remapping in order to
+ * emulate quirks of terminals that today can be only found in museums.
+ */
+static int
+input_key_vt10x(struct bufferevent *bev, key_code key)
+{
+	struct utf8_data	 ud;
+	key_code		 onlykey;
+	char			*p;
+	static const char	*standard_map[2] = {
+		"1!9(0)=+;:'\",<.>/-8? 2",
+		"119900=+;;'',,..\x1f\x1f\x7f\x7f\0\0",
+	};
+
+	log_debug("%s: key in %llx", __func__, key);
+
+	if (key & KEYC_META)
+		input_key_write(__func__, bev, "\033", 1);
+
+	/*
+	 * There's no way to report modifiers for unicode keys in standard mode
+	 * so lose the modifiers.
+	 */
+	if (KEYC_IS_UNICODE(key)) {
+		utf8_to_data(key, &ud);
+                input_key_write(__func__, bev, ud.data, ud.size);
+		return (0);
+	}
+
+	onlykey = key & KEYC_MASK_KEY;
+
+	/* Prevent TAB and RET from being swallowed by C0 remapping logic. */
+	if (onlykey == '\r' || onlykey == '\t')
+		key &= ~KEYC_CTRL;
+
+	/*
+	 * Convert keys with Ctrl modifier into corresponding C0 control codes,
+	 * with the exception of *some* keys, which are remapped into printable
+	 * ASCII characters.
+	 *
+	 * There is no special handling for Shift modifier, which is pretty
+	 * much redundant anyway, as no terminal will send <base key>|SHIFT,
+	 * but only <shifted key>|SHIFT.
+	 */
+	if (key & KEYC_CTRL) {
+		p = strchr(standard_map[0], onlykey);
+		if (p != NULL)
+			key = standard_map[1][p - standard_map[0]];
+		else if (onlykey >= '3' && onlykey <= '7')
+			key = onlykey - '\030';
+		else if (onlykey >= '@' && onlykey <= '~')
+			key = onlykey & 0x1f;
+		else
+			return (-1);
+	}
+
+	log_debug("%s: key out %llx", __func__, key);
+
+	ud.data[0] = key & 0x7f;
+	input_key_write(__func__, bev, &ud.data[0], 1);
+	return (0);
+}
+
+/* Pick keys that are reported as vt10x keys in modifyOtherKeys=1 mode. */
+static int
+input_key_mode1(struct bufferevent *bev, key_code key)
+{
+	key_code	 onlykey;
+
+	log_debug("%s: key in %llx", __func__, key);
+
+	/*
+	 * As per
+	 * https://invisible-island.net/xterm/modified-keys-us-pc105.html.
+	 */
+	onlykey = key & KEYC_MASK_KEY;
+	if ((key & (KEYC_META | KEYC_CTRL)) == KEYC_CTRL &&
+	    (onlykey == '/' || onlykey == '@' || onlykey == '^' ||
+	     (onlykey >= '2' && onlykey <= '8') ||
+	     (onlykey >= '@' && onlykey <= '~')))
+		return (input_key_vt10x(bev, key));
+
+	/*
+	 * A regular or shifted Unicode key + Meta. In the absence of a
+	 * standard to back this, we mimic what iTerm 2 does.
+	 */
+	if ((key & (KEYC_CTRL | KEYC_META)) == KEYC_META &&
+	    KEYC_IS_UNICODE(key))
+		return (input_key_vt10x(bev, key));
+
+	return (-1);
+}
+
 /* Translate a key code into an output key sequence. */
 int
 input_key(struct screen *s, struct bufferevent *bev, key_code key)
 {
 	struct input_key_entry	*ike = NULL;
-	key_code		 justkey, newkey, outkey, modifiers;
+	key_code		 newkey;
 	struct utf8_data	 ud;
-	char			 tmp[64], modifier;
 
 	/* Mouse keys need a pane. */
 	if (KEYC_IS_MOUSE(key))
@@ -455,36 +590,45 @@ input_key(struct screen *s, struct bufferevent *bev, key_code key)
 		key = newkey|(key & (KEYC_MASK_MODIFIERS|KEYC_MASK_FLAGS));
 	}
 
+	/* Is this backtab? */
+	if ((key & KEYC_MASK_KEY) == KEYC_BTAB) {
+		if (s->mode & EXTENDED_KEY_MODES) {
+			/* When in xterm extended mode, remap into S-Tab. */
+			key = '\011' | (key & ~KEYC_MASK_KEY) | KEYC_SHIFT;
+		} else {
+			/* Otherwise clear modifiers. */
+			key &= ~KEYC_MASK_MODIFIERS;
+		}
+	}
+
 	/*
-	 * If this is a normal 7-bit key, just send it, with a leading escape
-	 * if necessary. If it is a UTF-8 key, split it and send it.
+	 * A trivial case, that is a 7-bit key, excluding C0 control characters
+	 * that can't be entered from the keyboard, and no modifiers; or a UTF-8
+	 * key and no modifiers.
 	 */
-	justkey = (key & ~(KEYC_META|KEYC_IMPLIED_META));
-	if (justkey <= 0x7f) {
-		if (key & KEYC_META)
-			input_key_write(__func__, bev, "\033", 1);
-		ud.data[0] = justkey;
-		input_key_write(__func__, bev, &ud.data[0], 1);
-		return (0);
-	}
-	if (KEYC_IS_UNICODE(justkey)) {
-		if (key & KEYC_META)
-			input_key_write(__func__, bev, "\033", 1);
-		utf8_to_data(justkey, &ud);
-		input_key_write(__func__, bev, ud.data, ud.size);
-		return (0);
+	if (!(key & ~KEYC_MASK_KEY)) {
+		if (key == C0_BS || key == C0_HT ||
+		    key == C0_CR || key == C0_ESC ||
+		    (key >= 0x20 && key <= 0x7f)) {
+			ud.data[0] = key;
+			input_key_write(__func__, bev, &ud.data[0], 1);
+			return (0);
+		}
+		if (KEYC_IS_UNICODE(key)) {
+			utf8_to_data(key, &ud);
+			input_key_write(__func__, bev, ud.data, ud.size);
+			return (0);
+		}
 	}
 
 	/*
-	 * Look up in the tree. If not in application keypad or cursor mode,
-	 * remove the flags from the key.
+	 * Look up the standard VT10x keys in the tree. If not in application
+	 * keypad or cursor mode, remove the respective flags from the key.
 	 */
 	if (~s->mode & MODE_KKEYPAD)
 		key &= ~KEYC_KEYPAD;
 	if (~s->mode & MODE_KCURSOR)
 		key &= ~KEYC_CURSOR;
-	if (s->mode & MODE_KEXTENDED)
-		ike = input_key_get(key|KEYC_EXTENDED);
 	if (ike == NULL)
 		ike = input_key_get(key);
 	if (ike == NULL && (key & KEYC_META) && (~key & KEYC_IMPLIED_META))
@@ -493,10 +637,9 @@ input_key(struct screen *s, struct bufferevent *bev, key_code key)
 		ike = input_key_get(key & ~KEYC_CURSOR);
 	if (ike == NULL && (key & KEYC_KEYPAD))
 		ike = input_key_get(key & ~KEYC_KEYPAD);
-	if (ike == NULL && (key & KEYC_EXTENDED))
-		ike = input_key_get(key & ~KEYC_EXTENDED);
 	if (ike != NULL) {
-		log_debug("found key 0x%llx: \"%s\"", key, ike->data);
+		log_debug("%s: found key 0x%llx: \"%s\"", __func__, key,
+		    ike->data);
 		if ((key == KEYC_PASTE_START || key == KEYC_PASTE_END) &&
 		    (~s->mode & MODE_BRACKETPASTE))
 			return (0);
@@ -506,78 +649,34 @@ input_key(struct screen *s, struct bufferevent *bev, key_code key)
 		return (0);
 	}
 
-	/* No builtin key sequence; construct an extended key sequence. */
-	if (~s->mode & MODE_KEXTENDED) {
-		if ((key & KEYC_MASK_MODIFIERS) != KEYC_CTRL)
-			goto missing;
-		justkey = (key & KEYC_MASK_KEY);
-		switch (justkey) {
-		case ' ':
-		case '2':
-			key = 0|(key & ~KEYC_MASK_KEY);
-			break;
-		case '|':
-			key = 28|(key & ~KEYC_MASK_KEY);
-			break;
-		case '6':
-			key = 30|(key & ~KEYC_MASK_KEY);
-			break;
-		case '-':
-		case '/':
-			key = 31|(key & ~KEYC_MASK_KEY);
-			break;
-		case '?':
-			key = 127|(key & ~KEYC_MASK_KEY);
-			break;
-		default:
-			if (justkey >= 'A' && justkey <= '_')
-				key = (justkey - 'A')|(key & ~KEYC_MASK_KEY);
-			else if (justkey >= 'a' && justkey <= '~')
-				key = (justkey - 96)|(key & ~KEYC_MASK_KEY);
-			else
-				return (0);
-			break;
-		}
-		return (input_key(s, bev, key & ~KEYC_CTRL));
-	}
-	outkey = (key & KEYC_MASK_KEY);
-	modifiers = (key & KEYC_MASK_MODIFIERS);
-	if (outkey < 32 && outkey != 9 && outkey != 13 && outkey != 27) {
-		outkey = 64 + outkey;
-		modifiers |= KEYC_CTRL;
-	}
-	switch (modifiers) {
-	case KEYC_SHIFT:
-		modifier = '2';
-		break;
-	case KEYC_META:
-		modifier = '3';
-		break;
-	case KEYC_SHIFT|KEYC_META:
-		modifier = '4';
-		break;
-	case KEYC_CTRL:
-		modifier = '5';
-		break;
-	case KEYC_SHIFT|KEYC_CTRL:
-		modifier = '6';
-		break;
-	case KEYC_META|KEYC_CTRL:
-		modifier = '7';
-		break;
-	case KEYC_SHIFT|KEYC_META|KEYC_CTRL:
-		modifier = '8';
-		break;
+	/*
+	 * No builtin key sequence; construct an extended key sequence
+	 * depending on the client mode.
+	 *
+	 * If something invalid reaches here, an invalid output may be
+	 * produced. For example Ctrl-Shift-2 is invalid (as there's
+	 * no way to enter it). The correct form is Ctrl-Shift-@, at
+	 * least in US English keyboard layout.
+	 */
+	switch (s->mode & EXTENDED_KEY_MODES) {
+	case MODE_KEYS_EXTENDED_2:
+		/*
+		 * The simplest mode to handle - *all* modified keys are
+		 * reported in the extended form.
+		 */
+		return (input_key_extended(bev, key));
+        case MODE_KEYS_EXTENDED:
+		/*
+		 * Some keys are still reported in standard mode, to maintain
+		 * compatibility with applications unaware of extended keys.
+		 */
+		if (input_key_mode1(bev, key) == -1)
+			return (input_key_extended(bev, key));
+		return (0);
 	default:
-		goto missing;
+		/* The standard mode. */
+		return (input_key_vt10x(bev, key));
 	}
-	xsnprintf(tmp, sizeof tmp, "\033[%llu;%cu", outkey, modifier);
-	input_key_write(__func__, bev, tmp, strlen(tmp));
-	return (0);
-
-missing:
-	log_debug("key 0x%llx missing", key);
-	return (-1);
 }
 
 /* Get mouse event string. */
diff --git a/usr.bin/tmux/input.c b/usr.bin/tmux/input.c
index 00268e8e933..eb23e89c7f7 100644
--- a/usr.bin/tmux/input.c
+++ b/usr.bin/tmux/input.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: input.c,v 1.226 2024/08/19 08:31:36 nicm Exp $ */
+/* $OpenBSD: input.c,v 1.227 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1408,17 +1408,29 @@ input_csi_dispatch(struct input_ctx *ictx)
 	case INPUT_CSI_MODSET:
 		n = input_get(ictx, 0, 0, 0);
 		m = input_get(ictx, 1, 0, 0);
+		/*
+		 * Set the extended key reporting mode as per the client request,
+		 * unless "extended-keys always" forces us into mode 1.
+		 */
 		if (options_get_number(global_options, "extended-keys") == 2)
 			break;
-		if (n == 0 || (n == 4 && m == 0))
-			screen_write_mode_clear(sctx, MODE_KEXTENDED);
-		else if (n == 4 && (m == 1 || m == 2))
-			screen_write_mode_set(sctx, MODE_KEXTENDED);
+		screen_write_mode_clear(sctx,
+		    MODE_KEYS_EXTENDED|MODE_KEYS_EXTENDED_2);
+		if (n == 4 && m == 1)
+			screen_write_mode_set(sctx, MODE_KEYS_EXTENDED);
+		if (n == 4 && m == 2)
+			screen_write_mode_set(sctx, MODE_KEYS_EXTENDED_2);
 		break;
 	case INPUT_CSI_MODOFF:
 		n = input_get(ictx, 0, 0, 0);
-		if (n == 4)
-			screen_write_mode_clear(sctx, MODE_KEXTENDED);
+		/*
+		 * Clear the extended key reporting mode as per the client request,
+		 * unless "extended-keys always" forces us into mode 1.
+		 */
+		if (n == 4) {
+			screen_write_mode_clear(sctx,
+			    MODE_KEYS_EXTENDED|MODE_KEYS_EXTENDED_2);
+		}
 		break;
 	case INPUT_CSI_WINOPS:
 		input_csi_dispatch_winops(ictx);
diff --git a/usr.bin/tmux/key-string.c b/usr.bin/tmux/key-string.c
index 9b22d2ea101..d9ba95afae6 100644
--- a/usr.bin/tmux/key-string.c
+++ b/usr.bin/tmux/key-string.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: key-string.c,v 1.71 2023/01/16 11:26:14 nicm Exp $ */
+/* $OpenBSD: key-string.c,v 1.72 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -56,12 +56,47 @@ static const struct {
 	{ "PPage",	KEYC_PPAGE|KEYC_IMPLIED_META },
 	{ "PageUp",	KEYC_PPAGE|KEYC_IMPLIED_META },
 	{ "PgUp",	KEYC_PPAGE|KEYC_IMPLIED_META },
-	{ "Tab",	'\011' },
 	{ "BTab",	KEYC_BTAB },
 	{ "Space",	' ' },
 	{ "BSpace",	KEYC_BSPACE },
-	{ "Enter",	'\r' },
-	{ "Escape",	'\033' },
+
+	/*
+	 * C0 control characters, with the exception of Tab, Enter,
+	 * and Esc, should never appear as keys. We still render them,
+	 * so to be able to spot them in logs in case of an abnormality.
+	 */
+	{ "[NUL]",	C0_NUL },
+	{ "[SOH]",	C0_SOH },
+	{ "[STX]",	C0_STX },
+	{ "[ETX]",	C0_ETX },
+	{ "[EOT]",	C0_EOT },
+	{ "[ENQ]",	C0_ENQ },
+	{ "[ASC]",	C0_ASC },
+	{ "[BEL]",	C0_BEL },
+	{ "[BS]",	C0_BS },
+	{ "Tab",	C0_HT },
+	{ "[LF]",	C0_LF },
+	{ "[VT]",	C0_VT },
+	{ "[FF]",	C0_FF },
+	{ "Enter",	C0_CR },
+	{ "[SO]",	C0_SO },
+	{ "[SI]",	C0_SI },
+	{ "[DLE]",	C0_DLE },
+	{ "[DC1]",	C0_DC1 },
+	{ "[DC2]",	C0_DC2 },
+	{ "[DC3]",	C0_DC3 },
+	{ "[DC4]",	C0_DC4 },
+	{ "[NAK]",	C0_NAK },
+	{ "[SYN]",	C0_SYN },
+	{ "[ETB]",	C0_ETB },
+	{ "[CAN]",	C0_CAN },
+	{ "[EM]",	C0_EM },
+	{ "[SUB]",	C0_SUB },
+	{ "Escape",	C0_ESC },
+	{ "[FS]",	C0_FS },
+	{ "[GS]",	C0_GS },
+	{ "[RS]",	C0_RS },
+	{ "[US]",	C0_US },
 
 	/* Arrow keys. */
 	{ "Up",		KEYC_UP|KEYC_CURSOR|KEYC_IMPLIED_META },
@@ -206,7 +241,6 @@ key_string_get_modifiers(const char **string)
 key_code
 key_string_lookup_string(const char *string)
 {
-	static const char	*other = "!#()+,-.0123456789:;<=>'\r\t\177`/";
 	key_code		 key, modifiers;
 	u_int			 u, i;
 	struct utf8_data	 ud, *udp;
@@ -281,26 +315,6 @@ key_string_lookup_string(const char *string)
 			key &= ~KEYC_IMPLIED_META;
 	}
 
-	/* Convert the standard control keys. */
-	if (key <= 127 &&
-	    (modifiers & KEYC_CTRL) &&
-	    strchr(other, key) == NULL &&
-	    key != 9 &&
-	    key != 13 &&
-	    key != 27) {
-		if (key >= 97 && key <= 122)
-			key -= 96;
-		else if (key >= 64 && key <= 95)
-                       key -= 64;
-		else if (key == 32)
-			key = 0;
-		else if (key == 63)
-			key = 127;
-		else
-			return (KEYC_UNKNOWN);
-		modifiers &= ~KEYC_CTRL;
-	}
-
 	return (key|modifiers);
 }
 
@@ -324,10 +338,6 @@ key_string_lookup_key(key_code key, int with_flags)
 		goto out;
 	}
 
-	/* Display C-@ as C-Space. */
-	if ((key & (KEYC_MASK_KEY|KEYC_MASK_MODIFIERS)) == 0)
-		key = ' '|KEYC_CTRL;
-
 	/* Fill in the modifiers. */
 	if (key & KEYC_CTRL)
 		strlcat(out, "C-", sizeof out);
@@ -427,13 +437,8 @@ key_string_lookup_key(key_code key, int with_flags)
 		goto out;
 	}
 
-	/* Check for standard or control key. */
-	if (key <= 32) {
-		if (key == 0 || key > 26)
-			xsnprintf(tmp, sizeof tmp, "C-%c", (int)(64 + key));
-		else
-			xsnprintf(tmp, sizeof tmp, "C-%c", (int)(96 + key));
-	} else if (key >= 32 && key <= 126) {
+	/* Printable ASCII keys. */
+	if (key > 32 && key <= 126) {
 		tmp[0] = key;
 		tmp[1] = '\0';
 	} else if (key == 127)
@@ -460,8 +465,6 @@ out:
 			strlcat(out, "I", sizeof out);
 		if (saved & KEYC_BUILD_MODIFIERS)
 			strlcat(out, "B", sizeof out);
-		if (saved & KEYC_EXTENDED)
-			strlcat(out, "E", sizeof out);
 		if (saved & KEYC_SENT)
 			strlcat(out, "S", sizeof out);
 		strlcat(out, "]", sizeof out);
diff --git a/usr.bin/tmux/menu.c b/usr.bin/tmux/menu.c
index 79ad009ffdc..10ad6646937 100644
--- a/usr.bin/tmux/menu.c
+++ b/usr.bin/tmux/menu.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: menu.c,v 1.52 2023/08/15 07:01:47 nicm Exp $ */
+/* $OpenBSD: menu.c,v 1.53 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2019 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -335,7 +335,7 @@ menu_key_cb(struct client *c, void *data, struct key_event *event)
 		c->flags |= CLIENT_REDRAWOVERLAY;
 		return (0);
 	case KEYC_PPAGE:
-	case '\002': /* C-b */
+	case 'b'|KEYC_CTRL:
 		if (md->choice < 6)
 			md->choice = 0;
 		else {
@@ -394,13 +394,13 @@ menu_key_cb(struct client *c, void *data, struct key_event *event)
 		}
 		c->flags |= CLIENT_REDRAWOVERLAY;
 		break;
-	case '\006': /* C-f */
+	case 'f'|KEYC_CTRL:
 		break;
 	case '\r':
 		goto chosen;
 	case '\033': /* Escape */
-	case '\003': /* C-c */
-	case '\007': /* C-g */
+	case 'c'|KEYC_CTRL:
+	case 'g'|KEYC_CTRL:
 	case 'q':
 		return (1);
 	}
diff --git a/usr.bin/tmux/mode-tree.c b/usr.bin/tmux/mode-tree.c
index 8c62602428b..41c220100ca 100644
--- a/usr.bin/tmux/mode-tree.c
+++ b/usr.bin/tmux/mode-tree.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: mode-tree.c,v 1.68 2024/08/04 08:53:43 nicm Exp $ */
+/* $OpenBSD: mode-tree.c,v 1.69 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2017 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1088,22 +1088,22 @@ mode_tree_key(struct mode_tree_data *mtd, struct client *c, key_code *key,
 	switch (*key) {
 	case 'q':
 	case '\033': /* Escape */
-	case '\007': /* C-g */
+	case 'g'|KEYC_CTRL:
 		return (1);
 	case KEYC_UP:
 	case 'k':
 	case KEYC_WHEELUP_PANE:
-	case '\020': /* C-p */
+	case 'p'|KEYC_CTRL:
 		mode_tree_up(mtd, 1);
 		break;
 	case KEYC_DOWN:
 	case 'j':
 	case KEYC_WHEELDOWN_PANE:
-	case '\016': /* C-n */
+	case 'n'|KEYC_CTRL:
 		mode_tree_down(mtd, 1);
 		break;
 	case KEYC_PPAGE:
-	case '\002': /* C-b */
+	case 'b'|KEYC_CTRL:
 		for (i = 0; i < mtd->height; i++) {
 			if (mtd->current == 0)
 				break;
@@ -1111,7 +1111,7 @@ mode_tree_key(struct mode_tree_data *mtd, struct client *c, key_code *key,
 		}
 		break;
 	case KEYC_NPAGE:
-	case '\006': /* C-f */
+	case 'f'|KEYC_CTRL:
 		for (i = 0; i < mtd->height; i++) {
 			if (mtd->current == mtd->line_size - 1)
 				break;
@@ -1155,7 +1155,7 @@ mode_tree_key(struct mode_tree_data *mtd, struct client *c, key_code *key,
 		for (i = 0; i < mtd->line_size; i++)
 			mtd->line_list[i].item->tagged = 0;
 		break;
-	case '\024': /* C-t */
+	case 't'|KEYC_CTRL:
 		for (i = 0; i < mtd->line_size; i++) {
 			if ((mtd->line_list[i].item->parent == NULL &&
 			    !mtd->line_list[i].item->no_tag) ||
@@ -1211,7 +1211,7 @@ mode_tree_key(struct mode_tree_data *mtd, struct client *c, key_code *key,
 		break;
 	case '?':
 	case '/':
-	case '\023': /* C-s */
+	case 's'|KEYC_CTRL:
 		mtd->references++;
 		status_prompt_set(c, NULL, "(search) ", "",
 		    mode_tree_search_callback, mode_tree_search_free, mtd,
diff --git a/usr.bin/tmux/options-table.c b/usr.bin/tmux/options-table.c
index f1e85609206..dd1782bc280 100644
--- a/usr.bin/tmux/options-table.c
+++ b/usr.bin/tmux/options-table.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: options-table.c,v 1.175 2024/08/04 09:35:30 nicm Exp $ */
+/* $OpenBSD: options-table.c,v 1.176 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2011 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -94,6 +94,9 @@ static const char *options_table_detach_on_destroy_list[] = {
 static const char *options_table_extended_keys_list[] = {
 	"off", "on", "always", NULL
 };
+static const char *options_table_extended_keys_format_list[] = {
+	"csi-u", "xterm", NULL
+};
 static const char *options_table_allow_passthrough_list[] = {
 	"off", "on", "all", NULL
 };
@@ -310,11 +313,19 @@ const struct options_table_entry options_table[] = {
 	  .type = OPTIONS_TABLE_CHOICE,
 	  .scope = OPTIONS_TABLE_SERVER,
 	  .choices = options_table_extended_keys_list,
-	  .default_num = 0,
+	  .default_num = 1,
 	  .text = "Whether to request extended key sequences from terminals "
 		  "that support it."
 	},
 
+	{ .name = "extended-keys-format",
+	  .type = OPTIONS_TABLE_CHOICE,
+	  .scope = OPTIONS_TABLE_SERVER,
+	  .choices = options_table_extended_keys_format_list,
+	  .default_num = 1,
+	  .text = "The format of emitted extended key sequences."
+	},
+
 	{ .name = "focus-events",
 	  .type = OPTIONS_TABLE_FLAG,
 	  .scope = OPTIONS_TABLE_SERVER,
@@ -614,7 +625,7 @@ const struct options_table_entry options_table[] = {
 	{ .name = "prefix",
 	  .type = OPTIONS_TABLE_KEY,
 	  .scope = OPTIONS_TABLE_SESSION,
-	  .default_num = '\002',
+	  .default_num = 'b'|KEYC_CTRL,
 	  .text = "The prefix key."
 	},
 
diff --git a/usr.bin/tmux/popup.c b/usr.bin/tmux/popup.c
index 8f543f83f20..81d749d8009 100644
--- a/usr.bin/tmux/popup.c
+++ b/usr.bin/tmux/popup.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: popup.c,v 1.53 2024/03/21 11:30:42 nicm Exp $ */
+/* $OpenBSD: popup.c,v 1.54 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2020 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -543,7 +543,7 @@ popup_key_cb(struct client *c, void *data, struct key_event *event)
 	}
 	if ((((pd->flags & (POPUP_CLOSEEXIT|POPUP_CLOSEEXITZERO)) == 0) ||
 	    pd->job == NULL) &&
-	    (event->key == '\033' || event->key == '\003'))
+	    (event->key == '\033' || event->key == ('c'|KEYC_CTRL)))
 		return (1);
 	if (pd->job != NULL) {
 		if (KEYC_IS_MOUSE(event->key)) {
diff --git a/usr.bin/tmux/screen-write.c b/usr.bin/tmux/screen-write.c
index 350ff672b9f..17dfb1d33cb 100644
--- a/usr.bin/tmux/screen-write.c
+++ b/usr.bin/tmux/screen-write.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: screen-write.c,v 1.225 2024/03/21 12:10:57 nicm Exp $ */
+/* $OpenBSD: screen-write.c,v 1.226 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -326,8 +326,9 @@ screen_write_reset(struct screen_write_ctx *ctx)
 	screen_write_scrollregion(ctx, 0, screen_size_y(s) - 1);
 
 	s->mode = MODE_CURSOR|MODE_WRAP;
+
 	if (options_get_number(global_options, "extended-keys") == 2)
-		s->mode |= MODE_KEXTENDED;
+		s->mode = (s->mode & ~EXTENDED_KEY_MODES)|MODE_KEYS_EXTENDED;
 
 	screen_write_clearscreen(ctx, 8);
 	screen_write_set_cursor(ctx, 0, 0);
diff --git a/usr.bin/tmux/screen.c b/usr.bin/tmux/screen.c
index ff73a8c4e72..182d6a89428 100644
--- a/usr.bin/tmux/screen.c
+++ b/usr.bin/tmux/screen.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: screen.c,v 1.85 2024/03/21 11:26:28 nicm Exp $ */
+/* $OpenBSD: screen.c,v 1.86 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -107,8 +107,9 @@ screen_reinit(struct screen *s)
 	s->rlower = screen_size_y(s) - 1;
 
 	s->mode = MODE_CURSOR|MODE_WRAP|(s->mode & MODE_CRLF);
+
 	if (options_get_number(global_options, "extended-keys") == 2)
-		s->mode |= MODE_KEXTENDED;
+		s->mode = (s->mode & ~EXTENDED_KEY_MODES)|MODE_KEYS_EXTENDED;
 
 	if (s->saved_grid != NULL)
 		screen_alternate_off(s, NULL, 0);
@@ -714,8 +715,10 @@ screen_mode_to_string(int mode)
 		strlcat(tmp, "ORIGIN,", sizeof tmp);
 	if (mode & MODE_CRLF)
 		strlcat(tmp, "CRLF,", sizeof tmp);
-	if (mode & MODE_KEXTENDED)
-		strlcat(tmp, "KEXTENDED,", sizeof tmp);
+	if (mode & MODE_KEYS_EXTENDED)
+		strlcat(tmp, "KEYS_EXTENDED,", sizeof tmp);
+	if (mode & MODE_KEYS_EXTENDED_2)
+		strlcat(tmp, "KEYS_EXTENDED_2,", sizeof tmp);
 	tmp[strlen(tmp) - 1] = '\0';
 	return (tmp);
 }
diff --git a/usr.bin/tmux/status.c b/usr.bin/tmux/status.c
index 5c75db37aeb..f85937fd961 100644
--- a/usr.bin/tmux/status.c
+++ b/usr.bin/tmux/status.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: status.c,v 1.242 2024/05/15 08:39:30 nicm Exp $ */
+/* $OpenBSD: status.c,v 1.243 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -839,19 +839,19 @@ status_prompt_translate_key(struct client *c, key_code key, key_code *new_key)
 {
 	if (c->prompt_mode == PROMPT_ENTRY) {
 		switch (key) {
-		case '\001': /* C-a */
-		case '\003': /* C-c */
-		case '\005': /* C-e */
-		case '\007': /* C-g */
-		case '\010': /* C-h */
+		case 'a'|KEYC_CTRL:
+		case 'c'|KEYC_CTRL:
+		case 'e'|KEYC_CTRL:
+		case 'g'|KEYC_CTRL:
+		case 'h'|KEYC_CTRL:
 		case '\011': /* Tab */
-		case '\013': /* C-k */
-		case '\016': /* C-n */
-		case '\020': /* C-p */
-		case '\024': /* C-t */
-		case '\025': /* C-u */
-		case '\027': /* C-w */
-		case '\031': /* C-y */
+		case 'k'|KEYC_CTRL:
+		case 'n'|KEYC_CTRL:
+		case 'p'|KEYC_CTRL:
+		case 't'|KEYC_CTRL:
+		case 'u'|KEYC_CTRL:
+		case 'w'|KEYC_CTRL:
+		case 'y'|KEYC_CTRL:
 		case '\n':
 		case '\r':
 		case KEYC_LEFT|KEYC_CTRL:
@@ -890,7 +890,7 @@ status_prompt_translate_key(struct client *c, key_code key, key_code *new_key)
 	case 'S':
 		c->prompt_mode = PROMPT_ENTRY;
 		c->flags |= CLIENT_REDRAWSTATUS;
-		*new_key = '\025'; /* C-u */
+		*new_key = 'u'|KEYC_CTRL;
 		return (1);
 	case 'i':
 	case '\033': /* Escape */
@@ -911,7 +911,7 @@ status_prompt_translate_key(struct client *c, key_code key, key_code *new_key)
 		return (1);
 	case 'C':
 	case 'D':
-		*new_key = '\013'; /* C-k */
+		*new_key = 'k'|KEYC_CTRL;
 		return (1);
 	case KEYC_BSPACE:
 	case 'X':
@@ -924,7 +924,7 @@ status_prompt_translate_key(struct client *c, key_code key, key_code *new_key)
 		*new_key = 'B'|KEYC_VI;
 		return (1);
 	case 'd':
-		*new_key = '\025'; /* C-u */
+		*new_key = 'u'|KEYC_CTRL;
 		return (1);
 	case 'e':
 		*new_key = 'e'|KEYC_VI;
@@ -939,10 +939,10 @@ status_prompt_translate_key(struct client *c, key_code key, key_code *new_key)
 		*new_key = 'W'|KEYC_VI;
 		return (1);
 	case 'p':
-		*new_key = '\031'; /* C-y */
+		*new_key = 'y'|KEYC_CTRL;
 		return (1);
 	case 'q':
-		*new_key = '\003'; /* C-c */
+		*new_key = 'c'|KEYC_CTRL;
 		return (1);
 	case 's':
 	case KEYC_DC:
@@ -966,8 +966,8 @@ status_prompt_translate_key(struct client *c, key_code key, key_code *new_key)
 	case 'k':
 		*new_key = KEYC_UP;
 		return (1);
-	case '\010' /* C-h */:
-	case '\003' /* C-c */:
+	case 'h'|KEYC_CTRL:
+	case 'c'|KEYC_CTRL:
 	case '\n':
 	case '\r':
 		return (1);
@@ -1263,28 +1263,28 @@ status_prompt_key(struct client *c, key_code key)
 process_key:
 	switch (key) {
 	case KEYC_LEFT:
-	case '\002': /* C-b */
+	case 'b'|KEYC_CTRL:
 		if (c->prompt_index > 0) {
 			c->prompt_index--;
 			break;
 		}
 		break;
 	case KEYC_RIGHT:
-	case '\006': /* C-f */
+	case 'f'|KEYC_CTRL:
 		if (c->prompt_index < size) {
 			c->prompt_index++;
 			break;
 		}
 		break;
 	case KEYC_HOME:
-	case '\001': /* C-a */
+	case 'a'|KEYC_CTRL:
 		if (c->prompt_index != 0) {
 			c->prompt_index = 0;
 			break;
 		}
 		break;
 	case KEYC_END:
-	case '\005': /* C-e */
+	case 'e'|KEYC_CTRL:
 		if (c->prompt_index != size) {
 			c->prompt_index = size;
 			break;
@@ -1295,7 +1295,7 @@ process_key:
 			goto changed;
 		break;
 	case KEYC_BSPACE:
-	case '\010': /* C-h */
+	case 'h'|KEYC_CTRL:
 		if (c->prompt_index != 0) {
 			if (c->prompt_index == size)
 				c->prompt_buffer[--c->prompt_index].size = 0;
@@ -1310,7 +1310,7 @@ process_key:
 		}
 		break;
 	case KEYC_DC:
-	case '\004': /* C-d */
+	case 'd'|KEYC_CTRL:
 		if (c->prompt_index != size) {
 			memmove(c->prompt_buffer + c->prompt_index,
 			    c->prompt_buffer + c->prompt_index + 1,
@@ -1319,17 +1319,17 @@ process_key:
 			goto changed;
 		}
 		break;
-	case '\025': /* C-u */
+	case 'u'|KEYC_CTRL:
 		c->prompt_buffer[0].size = 0;
 		c->prompt_index = 0;
 		goto changed;
-	case '\013': /* C-k */
+	case 'k'|KEYC_CTRL:
 		if (c->prompt_index < size) {
 			c->prompt_buffer[c->prompt_index].size = 0;
 			goto changed;
 		}
 		break;
-	case '\027': /* C-w */
+	case 'w'|KEYC_CTRL:
 		separators = options_get_string(oo, "word-separators");
 		idx = c->prompt_index;
 
@@ -1397,7 +1397,7 @@ process_key:
 		status_prompt_backward_word(c, separators);
 		goto changed;
 	case KEYC_UP:
-	case '\020': /* C-p */
+	case 'p'|KEYC_CTRL:
 		histstr = status_prompt_up_history(c->prompt_hindex,
 		    c->prompt_type);
 		if (histstr == NULL)
@@ -1407,7 +1407,7 @@ process_key:
 		c->prompt_index = utf8_strlen(c->prompt_buffer);
 		goto changed;
 	case KEYC_DOWN:
-	case '\016': /* C-n */
+	case 'n'|KEYC_CTRL:
 		histstr = status_prompt_down_history(c->prompt_hindex,
 		    c->prompt_type);
 		if (histstr == NULL)
@@ -1416,11 +1416,11 @@ process_key:
 		c->prompt_buffer = utf8_fromcstr(histstr);
 		c->prompt_index = utf8_strlen(c->prompt_buffer);
 		goto changed;
-	case '\031': /* C-y */
+	case 'y'|KEYC_CTRL:
 		if (status_prompt_paste(c))
 			goto changed;
 		break;
-	case '\024': /* C-t */
+	case 't'|KEYC_CTRL:
 		idx = c->prompt_index;
 		if (idx < size)
 			idx++;
@@ -1443,12 +1443,12 @@ process_key:
 		free(s);
 		break;
 	case '\033': /* Escape */
-	case '\003': /* C-c */
-	case '\007': /* C-g */
+	case 'c'|KEYC_CTRL:
+	case 'g'|KEYC_CTRL:
 		if (c->prompt_inputcb(c, c->prompt_data, NULL, 1) == 0)
 			status_prompt_clear(c);
 		break;
-	case '\022': /* C-r */
+	case 'r'|KEYC_CTRL:
 		if (~c->prompt_flags & PROMPT_INCREMENTAL)
 			break;
 		if (c->prompt_buffer[0].size == 0) {
@@ -1459,7 +1459,7 @@ process_key:
 		} else
 			prefix = '-';
 		goto changed;
-	case '\023': /* C-s */
+	case 's'|KEYC_CTRL:
 		if (~c->prompt_flags & PROMPT_INCREMENTAL)
 			break;
 		if (c->prompt_buffer[0].size == 0) {
diff --git a/usr.bin/tmux/tmux.1 b/usr.bin/tmux/tmux.1
index 11ac32c62db..983383c4f74 100644
--- a/usr.bin/tmux/tmux.1
+++ b/usr.bin/tmux/tmux.1
@@ -1,4 +1,4 @@
-.\" $OpenBSD: tmux.1,v 1.947 2024/08/04 09:01:18 nicm Exp $
+.\" $OpenBSD: tmux.1,v 1.948 2024/08/21 04:17:09 nicm Exp $
 .\"
 .\" Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
 .\"
@@ -14,7 +14,7 @@
 .\" IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 .\" OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: August 4 2024 $
+.Dd $Mdocdate: August 21 2024 $
 .Dt TMUX 1
 .Os
 .Sh NAME
@@ -3733,6 +3733,10 @@ Note that aliases are expanded when a command is parsed rather than when it is
 executed, so binding an alias with
 .Ic bind-key
 will bind the expanded form.
+.It Ic copy-command Ar shell-command
+Give the command to pipe to if the
+.Ic copy-pipe
+copy mode command is used without arguments.
 .It Ic default-terminal Ar terminal
 Set the default terminal for new windows created in this session - the
 default value of the
@@ -3746,10 +3750,6 @@ be set to
 .Ql screen ,
 .Ql tmux
 or a derivative of them.
-.It Ic copy-command Ar shell-command
-Give the command to pipe to if the
-.Ic copy-pipe
-copy mode command is used without arguments.
 .It Ic escape-time Ar time
 Set the time in milliseconds for which
 .Nm
@@ -3771,22 +3771,53 @@ If enabled, the server will exit when there are no attached clients.
 .It Xo Ic extended-keys
 .Op Ic on | off | always
 .Xc
-When
-.Ic on
-or
-.Ic always ,
-the escape sequence to enable extended keys is sent to the terminal, if
-.Nm
-knows that it is supported.
-.Nm
-always recognises extended keys itself.
-If this option is
+Controls how modified keys (keys pressed together with Control, Meta, or Shift)
+are reported.
+This is the equivalent of the
+.Ic modifyOtherKeys
+.Xr xterm 1
+resource.
+.Pp
+When set to
 .Ic on ,
-.Nm
-will only forward extended keys to applications when they request them; if
+the program inside the pane can request one of two modes: mode 1 which changes
+the sequence for only keys which lack an existing well-known representation; or
+mode 2 which changes the sequence for all keys.
+When set to
 .Ic always ,
+mode 1 output is forced and the program cannot change it.
+When set to
+.Ic off ,
+this feature is disabled and only standard keys are reported.
+.Pp
 .Nm
-will always forward the keys.
+will always request extended keys itself if the terminal supports them.
+See also the
+.Ic extkeys
+feature for the
+.Ic terminal-features
+option, the
+.Ic extended-keys-format
+option and the
+.Ic pane_key_mode
+variable.
+.It Xo Ic extended-keys-format
+.Op Ic csi-u | xterm
+.Xc
+Selects one of the two possible formats for reporting modified keys to
+applications.
+This is the equivalent of the
+.Ic formatOtherKeys
+.Xr xterm 1
+resource.
+For example, C-S-a will be reported as
+.Ql ^[[27;6;65~
+when set to
+.Ic xterm ,
+and as
+.Ql ^[[65;6u
+when set to
+.Ic csi-u .
 .It Xo Ic focus-events
 .Op Ic on | off
 .Xc
@@ -5512,6 +5543,7 @@ The following variables are available, where appropriate:
 .It Li "pane_in_mode" Ta "" Ta "1 if pane is in a mode"
 .It Li "pane_index" Ta "#P" Ta "Index of pane"
 .It Li "pane_input_off" Ta "" Ta "1 if input to pane is disabled"
+.It Li "pane_key_mode" Ta "" Ta "Extended key reporting mode in this pane"
 .It Li "pane_last" Ta "" Ta "1 if last pane"
 .It Li "pane_left" Ta "" Ta "Left of pane"
 .It Li "pane_marked" Ta "" Ta "1 if this is the marked pane"
diff --git a/usr.bin/tmux/tmux.h b/usr.bin/tmux/tmux.h
index a1ffc50b32f..7c6f7c7c84b 100644
--- a/usr.bin/tmux/tmux.h
+++ b/usr.bin/tmux/tmux.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: tmux.h,v 1.1220 2024/08/04 08:53:43 nicm Exp $ */
+/* $OpenBSD: tmux.h,v 1.1221 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -138,8 +138,7 @@ struct winlink;
 #define KEYC_IMPLIED_META    0x08000000000000ULL
 #define KEYC_BUILD_MODIFIERS 0x10000000000000ULL
 #define KEYC_VI		     0x20000000000000ULL
-#define KEYC_EXTENDED	     0x40000000000000ULL
-#define KEYC_SENT	     0x80000000000000ULL
+#define KEYC_SENT	     0x40000000000000ULL
 
 /* Masks for key bits. */
 #define KEYC_MASK_MODIFIERS  0x00f00000000000ULL
@@ -187,6 +186,42 @@ struct winlink;
  */
 typedef unsigned long long key_code;
 
+/* C0 control characters */
+enum {
+	C0_NUL,
+	C0_SOH,
+	C0_STX,
+	C0_ETX,
+	C0_EOT,
+	C0_ENQ,
+	C0_ASC,
+	C0_BEL,
+	C0_BS,
+	C0_HT,
+	C0_LF,
+	C0_VT,
+	C0_FF,
+	C0_CR,
+	C0_SO,
+	C0_SI,
+	C0_DLE,
+	C0_DC1,
+	C0_DC2,
+	C0_DC3,
+	C0_DC4,
+	C0_NAK,
+	C0_SYN,
+	C0_ETB,
+	C0_CAN,
+	C0_EM,
+	C0_SUB,
+	C0_ESC,
+	C0_FS,
+	C0_GS,
+	C0_RS,
+	C0_US
+};
+
 /* Special key codes. */
 enum {
 	/* Focus events. */
@@ -582,14 +617,16 @@ enum tty_code_code {
 #define MODE_MOUSE_ALL 0x1000
 #define MODE_ORIGIN 0x2000
 #define MODE_CRLF 0x4000
-#define MODE_KEXTENDED 0x8000
+#define MODE_KEYS_EXTENDED 0x8000
 #define MODE_CURSOR_VERY_VISIBLE 0x10000
 #define MODE_CURSOR_BLINKING_SET 0x20000
+#define MODE_KEYS_EXTENDED_2 0x40000
 
 #define ALL_MODES 0xffffff
 #define ALL_MOUSE_MODES (MODE_MOUSE_STANDARD|MODE_MOUSE_BUTTON|MODE_MOUSE_ALL)
 #define MOTION_MOUSE_MODES (MODE_MOUSE_BUTTON|MODE_MOUSE_ALL)
 #define CURSOR_MODES (MODE_CURSOR|MODE_CURSOR_BLINKING|MODE_CURSOR_VERY_VISIBLE)
+#define EXTENDED_KEY_MODES (MODE_KEYS_EXTENDED|MODE_KEYS_EXTENDED_2)
 
 /* Mouse protocol constants. */
 #define MOUSE_PARAM_MAX 0xff
diff --git a/usr.bin/tmux/tty-features.c b/usr.bin/tmux/tty-features.c
index 6e75ebcf2c9..3d5529fbfdd 100644
--- a/usr.bin/tmux/tty-features.c
+++ b/usr.bin/tmux/tty-features.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tty-features.c,v 1.30 2023/11/14 15:38:33 nicm Exp $ */
+/* $OpenBSD: tty-features.c,v 1.31 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2020 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -227,7 +227,7 @@ static const struct tty_feature tty_feature_sync = {
 
 /* Terminal supports extended keys. */
 static const char *const tty_feature_extkeys_capabilities[] = {
-	"Eneks=\\E[>4;1m",
+	"Eneks=\\E[>4;2m",
 	"Dseks=\\E[>4m",
 	NULL
 };
diff --git a/usr.bin/tmux/tty-keys.c b/usr.bin/tmux/tty-keys.c
index 67b7f5844e1..f859747e3c0 100644
--- a/usr.bin/tmux/tty-keys.c
+++ b/usr.bin/tmux/tty-keys.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tty-keys.c,v 1.176 2024/08/19 08:29:16 nicm Exp $ */
+/* $OpenBSD: tty-keys.c,v 1.177 2024/08/21 04:17:09 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -664,7 +664,7 @@ tty_keys_next(struct tty *tty)
 	size_t			 len, size;
 	cc_t			 bspace;
 	int			 delay, expired = 0, n;
-	key_code		 key;
+	key_code		 key, onlykey;
 	struct mouse_event	 m = { 0 };
 	struct key_event	*event;
 
@@ -801,6 +801,26 @@ first_key:
 		key = (u_char)buf[0];
 		size = 1;
 	}
+
+	/* C-Space is special. */
+	if ((key & KEYC_MASK_KEY) == C0_NUL)
+		key = ' ' | KEYC_CTRL | (key & KEYC_META);
+
+	/*
+	 * Fix up all C0 control codes that don't have a dedicated key into
+	 * corresponding Ctrl keys. Convert characters in the A-Z range into
+	 * lowercase, so ^A becomes a|CTRL.
+	 */
+	onlykey = key & KEYC_MASK_KEY;
+	if (onlykey < 0x20 && onlykey != C0_BS &&
+	    onlykey != C0_HT && onlykey != C0_CR &&
+	    onlykey != C0_ESC) {
+		onlykey |= 0x40;
+		if (onlykey >= 'A' && onlykey <= 'Z')
+			onlykey |= 0x20;
+		key = onlykey | KEYC_CTRL | (key & KEYC_META);
+	}
+
 	goto complete_key;
 
 partial_key:
@@ -910,7 +930,6 @@ tty_keys_extended_key(struct tty *tty, const char *buf, size_t len,
 	char		 tmp[64];
 	cc_t		 bspace;
 	key_code	 nkey;
-	key_code	 onlykey;
 	struct utf8_data ud;
 	utf8_char        uc;
 
@@ -974,7 +993,13 @@ tty_keys_extended_key(struct tty *tty, const char *buf, size_t len,
 	/* Update the modifiers. */
 	if (modifiers > 0) {
 		modifiers--;
-		if (modifiers & 1)
+		/*
+		 * The Shift modifier may not be reported in some input modes,
+		 * which is unfortunate, as in general case determining if a
+		 * character is shifted or not requires knowing the input
+		 * keyboard layout. So we only fix up the trivial case.
+		 */
+		if (modifiers & 1 || (nkey >= 'A' && nkey <= 'Z'))
 			nkey |= KEYC_SHIFT;
 		if (modifiers & 2)
 			nkey |= (KEYC_META|KEYC_IMPLIED_META); /* Alt */
@@ -984,34 +1009,15 @@ tty_keys_extended_key(struct tty *tty, const char *buf, size_t len,
 			nkey |= (KEYC_META|KEYC_IMPLIED_META); /* Meta */
 	}
 
-	/*
-	 * Don't allow both KEYC_CTRL and as an implied modifier. Also convert
-	 * C-X into C-x and so on.
-	 */
-	if (nkey & KEYC_CTRL) {
-		onlykey = (nkey & KEYC_MASK_KEY);
-		if (onlykey < 32 &&
-		    onlykey != 9 &&
-		    onlykey != 13 &&
-		    onlykey != 27)
-			/* nothing */;
-		else if (onlykey >= 97 && onlykey <= 122)
-			onlykey -= 96;
-		else if (onlykey >= 64 && onlykey <= 95)
-			onlykey -= 64;
-		else if (onlykey == 32)
-			onlykey = 0;
-		else if (onlykey == 63)
-			onlykey = 127;
-		else
-			onlykey |= KEYC_CTRL;
-		nkey = onlykey|((nkey & KEYC_MASK_MODIFIERS) & ~KEYC_CTRL);
-	}
+	/* Convert S-Tab into Backtab. */
+	if ((nkey & KEYC_MASK_KEY) == '\011' && (nkey & KEYC_SHIFT))
+		nkey = KEYC_BTAB | (nkey & ~KEYC_MASK_KEY & ~KEYC_SHIFT);
 
 	if (log_get_level() != 0) {
 		log_debug("%s: extended key %.*s is %llx (%s)", c->name,
 		    (int)*size, buf, nkey, key_string_lookup_key(nkey, 1));
 	}
+
 	*key = nkey;
 	return (0);
 }