code: private JsonToken scanUnquotedString(final char firstChar) {
          StringBuilder sb = new StringBuilder();
          sb.append(firstChar);
          int c = buffer.read();
          while (c == '$' || c == '_' || Character.isLetterOrDigit(c)) {
              sb.append((char) c);
              c = buffer.read();
          }
          buffer.unread(c);
          String lexeme = sb.toString();
          return new JsonToken(JsonTokenType.UNQUOTED_STRING, lexeme);
      }
docs: Reads {@code StringToken} from source.
  
  @return The string token.