code: def to_glyphs_kerning(self):
      
      for master_id, source in self._sources.items():
          for (left, right), value in source.font.kerning.items():
              left_match = UFO_KERN_GROUP_PATTERN.match(left)
              right_match = UFO_KERN_GROUP_PATTERN.match(right)
              if left_match:
                  left = "@MMK_L_{}".format(left_match.group(2))
              if right_match:
                  right = "@MMK_R_{}".format(right_match.group(2))
              self.font.setKerningForPair(master_id, left, right, value)
docs: Add UFO kerning to GSFont.