PangoCoverage  *
_pango_fc_font_map_fc_to_coverage (FcCharSet *charset)
{

  ...

  /* Awful hack so Hangul Tone marks get rendered with the same
   * font and in the same run as other Hangul characters. If a font
   * covers the first composed Hangul glyph, then it is declared to cover
   * the Hangul tone marks. This hack probably needs to be formalized
   * by choosing fonts for scripts rather than individual code points.
   */
  if (pango_coverage_get (coverage, 0xac00) == PANGO_COVERAGE_EXACT)
    {
      pango_coverage_set (coverage, 0x302e, PANGO_COVERAGE_EXACT);
      pango_coverage_set (coverage, 0x302f, PANGO_COVERAGE_EXACT);
    }

  return coverage;
}