Sets the size field of a font description in fractional points. This is mutually exclusive with pango_font_description_set_absolute_size().
the size of the font in points, scaled by PANGO_SCALE. (That is, a size value of 10 * PANGO_SCALE is a 10 point font. The conversion factor between points and device units depends on system configuration and the output device. For screen display, a logical DPI of 96 is common, in which case a 10 point font corresponds to a 10 * (96 / 72) = 13.3 pixel font. Use pango_font_description_set_absolute_size() if you need a particular size in device units.