@code{normal} orientation, 0.5 for @code{landscape} and
@code{opposing-landscape}.
@item
+@code{string-thickness-factor} -- Factor for changing thickness of each
+string in the fret diagram. Thickness of string @code{k} is given by
+@code{thickness}*(1+@code{string-thickness-factor})^(k-1). Default 0.
+@item
@code{top-fret-thickness} -- The thickness of the top fret line, as a multiple
of the standard thickness. Default value 3.
@item