Table defining how to output a glyph code to the frame.
If not nil, this is a vector indexed by glyph code to define the glyph.
Each element can be:
integer: a glyph code which this glyph is an alias for.
string: output this glyph using that string (not impl. in X windows).
nil: this glyph mod 524288 is the code of a character to output,
and this glyph / 524288 is the face number (see `face-id') to use
while outputting it.