Thinking out loud...
So, according to Alphanumeric article from Wikipedia:
In the POSIX/C[2] locale, there are either 36 (A-Z0-9, case insensitive) or 62 (A-Za-z0-9, case-sensitive) alphanumeric characters.
SliTaz uses UTF-8-based locales by default.
C locale is not equal en_US (en_US.UTF-8 if to be precise) because C locale using only ASCII character set, and not using other symbols, like €, or £, or ♣.
So, if we want to use any symbol without restriction, we wanted to switch to UTF-8 (read: switch to any SliTaz locale isatead of C).
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As for topic starter's question about "composition":
meydlo,
File /usr/share/X11/locale/en_US.UTF-8/Compose contains huge number of composition rules.
Many locales (in fact, not only en_US.UTF-8) used this file to compose symbols on user input (it does not matter—in console, in text editor, or in web browser).
All you need—is define Compose key (by default it absent on modern keyboards, so you need to re-define other one). Personally me prefere to use RightAlt key as Compose key. Here two ways to define it:
1. Edit/create (as root) file /etc/X11/xorg.conf.d/40-Keyboard.conf, here is my file:
Section "InputClass"
Identifier "Keyboard Defaults"
MatchIsKeyboard "yes"
Option "XkbLayout" "us,ru"
Option "XkbOptions" "grp:ctrl_shift_toggle, grp_led:scroll, compose:ralt, terminate:ctrl_alt_bksp"
EndSection
Reboot system to use new settings.
2. Use setxkbmap
setxkbmap -layout "us,ru" -option "grp:ctrl_shift_toggle,compose:ralt"
No need to reboot, changes are applied immediately. This line can be placed to the end of ~/.profile to execute it automatically on system logon.
Ok, now we have Compose key. How to use it?
Rules, described in /usr/share/X11/locale/en_US.UTF-8/Compose is not difficult to human reading (Multi_key is our Compose key):
Press (and release) Compose key, press (and release) "o" key and "c" key—you'll get Copyright sign ©
Main rule—compose symbol from simple symbols—looks like © is composed from letters "o" and "c"; "±" is composed from "+" and "-";
"¢" = "c" + "|";
"£" = "L" + "-";
"€" = "C" + "=" (or "=" + "C", or "c" + "=", or "E" + "="...)
Unicode U26×× symbols described too:
♩♪♫♬♭♮♯☭Ⓐ♥☺☹
Sad, but there is no rule to compose ♣ (but you can add your own compose rules).
I suggest you to use Character Map application: install gucharmap package.