They used to be in /usr/lib/X11/XKeysymDB or /usr/share/X11/XKeysymDB, but those have been missing from Ubuntu for a while. I've tried google, but all I get are more references to XKeysymDB or the outputs of different people's xmodmap -pke. Where is the concise list?
Probably the best up-to-date values for key symbol definitions is to look at the source-code.
Basically its just a list of keysym names with their associated codes.
sudo apt-get install x11proto-core-dev
Two key keyfiles in /usr/include/X11:
The main definition file:
/usr/include/X11/keysymdef.h
Vendor specific (i.e. Debian/Ubuntu):
/usr/include/X11/XF86keysym.h
There are a number of other header files in the same folder you can also examine:
$ grep -l '#define.*XK_' /usr/include/X11/*.h
Example definition from /usr/include/X11/keysymdef.h:
#define XK_BackSpace 0xff08 /* Back space, back char */
#define XK_Tab 0xff09
#define XK_Linefeed 0xff0a /* Linefeed, LF */
#define XK_Clear 0xff0b
#define XK_Return 0xff0d /* Return, enter */
#define XK_Pause 0xff13 /* Pause, hold */
#define XK_Scroll_Lock 0xff14
#define XK_Sys_Req 0xff15
#define XK_Escape 0xff1b
#define XK_Delete 0xffff /* Delete, rubout */
