The Window argument for the options that concern variable matrices is either matrix for some general options, or the matrix name, or a free variable. The latter specifies a value for all matrices.
default_font(Size, Font) :- concat_string(['-*-times-bold-r-normal-*-', Size, '-*-*-*-*-*-*-*'], Font).
[6,8,10,12,14,18,24]
WIDTHxHEIGHT+X+Y.Usually only X and Y are specified, because the matrix size is computed automatically.