(バージョン情報なし。おそらく SVN 版にしか存在しないでしょう)
CairoFontFace abstract class represents a particular font at a particular weight, slant, and other characteristic but no transformation or size.
Note: This class can not be instantiated directly, it is created by CairoContext::getFontFace() or cairo_scaled_font_get_font_face().