I have found out that my Debian menu system creates a $HOME/.rxvt/rxvt.menu file.

Trying to understand what's this file, i have discovered that rxvt should be able to display a menu, but even after reading /usr/share/doc/rxvt/html/rxvtRef.html i have not understood how to reach this menu.

Also a less important question regarding bash shell:

pressing alt+1, alt+2, alt+n i obtain a prompt
(arg: 1) : what is or where i can find info about this?

I have only found out that if i choose for example arg: 9 and i press for example i , i obtain iiiiiiiii .

Thanks in advance.

You have to know shell scripting to write an rxvt menu. I'm not sure about the arg1, etc.