actually implement suggestion on 9fans of earlier this year,
after seeing that cinap has already done so.

to recap <compose>x followed by 1-6 hex digits yields a rune
with the given codepoint.  if there are less than 6 hex digits, then
the terminating character is not represented in the output.

a difference from the previous suggestion is that the terminating
character need only be not a hex digit.

i think there are additional ideas that might be fruitful.  it would
be neat if a non-typing key like compose or shift would terminate,
then the terminating character could be included in the output.

Reference: /n/atom/patch/applied2013/composex
Date: Sat Oct 19 17:47:47 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/port/latin1.c	Sat Oct 19 17:42:22 2013
+++ /sys/src/9/port/latin1.c	Sat Oct 19 17:42:23 2013
@@ -46,7 +46,8 @@
  * failure, or something < -1 if n is too small.  In the latter case, the result
  * is minus the required n.
  */
-static	char	esctab[] = {'X', 5, 'Y', 7};
+static	char	esctab[] = {'X', 5, 5, 'Y', 7, 7, 'x', 7, 3};
+static	char	inset[] = "0123456789abcdefABCDEF";
 
 long
 latin1(Rune *k, int n)
@@ -55,10 +56,12 @@
 	int c, i;
 	char* p;
 
-	for(i = 0; i < nelem(esctab); i += 2)
+	for(i = 0; i < nelem(esctab); i += 3)
 		if(k[0] == esctab[i]){
 			if(n>=esctab[i+1])
 				return unicode(k, esctab[i+1]);
+			else if(n>=esctab[i+2] && strchr(inset, k[n-1]) == nil)
+				return unicode(k, n-1);
 			else
 				return -esctab[i+1];
 		}
--- /sys/src/nix/port/latin1.c	Sat Oct 19 17:42:24 2013
+++ /sys/src/nix/port/latin1.c	Sat Oct 19 17:42:24 2013
@@ -46,7 +46,8 @@
  * failure, or something < -1 if n is too small.  In the latter case, the result
  * is minus the required n.
  */
-static	char	esctab[] = {'X', 5, 'Y', 7};
+static	char	esctab[] = {'X', 5, 5, 'Y', 7, 7, 'x', 7, 3};
+static	char	inset[] = "0123456789abcdefABCDEF";
 
 long
 latin1(Rune *k, int n)
@@ -55,10 +56,12 @@
 	int c, i;
 	char* p;
 
-	for(i = 0; i < nelem(esctab); i += 2)
+	for(i = 0; i < nelem(esctab); i += 3)
 		if(k[0] == esctab[i]){
 			if(n>=esctab[i+1])
 				return unicode(k, esctab[i+1]);
+			else if(n>=esctab[i+2] && strchr(inset, k[n-1]) == nil)
+				return unicode(k, n-1);
 			else
 				return -esctab[i+1];
 		}
--- /sys/man/6/keyboard	Sat Oct 19 17:42:25 2013
+++ /sys/man/6/keyboard	Sat Oct 19 17:42:26 2013
@@ -89,11 +89,11 @@
 .L a
 to
 .LR f )
-or a capital
-.L Y
-and exactly six hexadecimal characters
-to type a single rune with the value represented by
-the typed number.
+or a lower case
+.L x
+followed by up to 6 hexadecimal characters.  If the sequence
+is shorter than 6 hexadecimal characters, the terminator will
+not appear in the output.
 There are shorthands for many characters, comprising
 the compose key followed by a two- or three-character sequence.
 There are several rules guiding the design of the sequences, as