Wt

The select elements does not support a placeholder attribute.

The correct way to implement this for WComboBox is to add a first option, and select this by default. So that the DOM tree looks like:

<select>
  <option value="-1" selected="selected" disabled>Placeholder text</option>
  <option value="0">Value 1</option>
  <option value="1">Value 2</option>
</select>

There, the option with value="-1" will be selected initially, on rendering, and will not be selectable by the user. This also implies that setting a placeholder will set the setNoSelectionEnabled(true).

For a WSelectionBox, a placeholder simply does not make any sense.