code: public final boolean append(String commandString, int nesting) {
        this.nesting += nesting;
        buffer.append(commandString);
        return this.nesting == 0;
     }
docs: Appends the new command.
  
  @param commandString the string with the command and arguments.
  @param nesting       the command nesting.
  @return {@code true} if the command(s) in buffer are ready to be sent.