void pango_font_description_set_variations ( PangoFontDescription* desc, const char* variations )
Sets the variations field of a font description.
OpenType font variations allow to select a font instance by specifying values for a number of axes, such as width or weight.
The format of the variations string is
with each AXIS a 4 character tag that identifies a font axis, and each VALUE a floating point number. Unknown axes are ignored, and values are clamped to their allowed range.
Pango does not currently have a way to find supported axes of a font. Both harfbuzz or freetype have API for this.