x-alt-keysym

x-alt-keysym is a variable defined in `C source code'.
Its value is

nil

Documentation:
Which keys Emacs uses for the alt modifier.
This should be one of the symbols `alt', `hyper', `meta', `super'.
For example, `alt' means use the Alt_L and Alt_R keysyms. The default
is nil, which is the same as `alt'.