code: void addField(final String name, final Object value)
              throws IllegalStateException {
  
          checkNotCompleted();
          _buffer.append(" <");
          _buffer.append(name);
          _buffer.append("=");
          _buffer.append(value);
          _buffer.append(">");
  
      }
docs: Adds a string representation of the given object field.
  
  @param name
  the name of the field
  @param value
  the value of the field
  @throws IllegalStateException
  if the string representation has already been completed