docs: private String forceAscii(StringBuilder source) {
  		int length = source.length();
  		StringBuilder res = new StringBuilder(length);
  		for (int i = 0; i < length; i++) {
  			char c = source.charAt(i);
  			if ((c >= SAFE_ASCII_LOWER && c <= SAFE_ASCII_UPPER) || Character.isSpaceChar(c)) {
  				res.append(c);
  			} else {
  				res.append("\\u");
  				String scode = Integer.toHexString(i);
  				while (scode.length() < 4) {
  					scode = "0" + scode;
  				}
  				res.append(scode);
  			}
  		}
  		return res.toString();
  	}