docs: private static String escape(char c) {
  		switch (c) {
  		case '\b':
  			return "\\b";
  		case '\t':
  			return "\\t";
  		case '\n':
  			return "\\n";
  		case '\f':
  			return "\\f";
  		case '\r':
  			return "\\r";
  		default:
  			if (c < StrUtil.C_SPACE || //
  					(c >= '\u0080' && c <= '\u00a0') || //
  					(c >= '\u2000' && c <= '\u2010') || //
  					(c >= '\u2028' && c <= '\u202F') || //
  					(c >= '\u2066' && c <= '\u206F')//
  			) {
  				return HexUtil.toUnicodeHex(c);
  			} else {
  				return Character.toString(c);
  			}
  		}
  	}