pango:font-description-variations (desc)

desc -- a pango:font-description instance
variations -- a string representing the variations

The pango:font-description-variations function gets the variations field of a font description. The (setf pango:font-description-variations) function sets the variations field. 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 AXIS1=VALUE, AXIS2=VALUE ..., 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 the HarfBuzz or FreeType libraries have API for this.