Modify fontset NAME to use FONT-SPEC for TARGET characters.
NAME is a fontset name string, nil for the fontset of FRAME, or t for
the default fontset.
TARGET may be a cons; (FROM . TO), where FROM and TO are characters.
In that case, use FONT-SPEC for all characters in the range FROM and
TARGET may be a script name symbol. In that case, use FONT-SPEC for
all characters that belong to the script.
TARGET may be a charset. In that case, use FONT-SPEC for all
characters in the charset.
TARGET may be nil. In that case, use FONT-SPEC for any characters for
that no FONT-SPEC is specified.
FONT-SPEC may one of these:
* A font-spec object made by the function `font-spec' (which see).
* A cons (FAMILY . REGISTRY), where FAMILY is a font family name and
REGISTRY is a font registry name. FAMILY may contain foundry
name, and REGISTRY may contain encoding name.
* A font name string.
* nil, which explicitly specifies that there's no font for TARGET.
Optional 4th argument FRAME is a frame or nil for the selected frame
that is concerned in the case that NAME is nil.
Optional 5th argument ADD, if non-nil, specifies how to add FONT-SPEC
to the font specifications for TARGET previously set. If it is
`prepend', FONT-SPEC is prepended. If it is `append', FONT-SPEC is appended. By default, FONT-SPEC overrides the previous settings. (fn NAME TARGET FONT-SPEC &optional FRAME ADD)