Function: ps-extend-face

Extend face in ALIST-SYM.

If optional MERGE-P is non-nil, extensions in FACE-EXTENSION list are merged
with face extensions in ALIST-SYM; otherwise, overrides.

If optional ALIST-SYM is nil, `ps-print-face-extension-alist' is used;
otherwise, it should be an alist symbol.

The elements of FACE-EXTENSION list have the form:


FACE-NAME is a face name symbol.

FOREGROUND and BACKGROUND may be nil or a string that denotes the
foreground and background colors respectively.

EXTENSION is one of the following symbols:
bold - use bold font.
italic - use italic font.
underline - put a line under text.
strikeout - like underline, but the line is in middle of text.
overline - like underline, but the line is over the text.
shadow - text will have a shadow.
box - text will be surrounded by a box.
outline - print characters as hollow outlines. If EXTENSION is any other symbol, it is ignored. (fn FACE-EXTENSION &optional MERGE-P ALIST-SYM)