code: @Nonnull
    @ReturnsMutableCopy
    public ICommonsList <CSSFontFaceRule> getAllFontFaceRules ()
    {
      return m_aRules.getAllMapped (r -> r instanceof CSSFontFaceRule, r -> (CSSFontFaceRule) r);
    }
docs: Get a list of all top-level rules that are font-face rules (implementing
  {@link CSSFontFaceRule}).
  
  @return A copy of all contained <code>@font-face</code> rules. Never
  <code>null</code>.