Below is a code snippet of how I am setting the value of a dropdown that is a single-selection dropdown. Can anyone tell me how you would set multiple values into the "value" property, is it simply a comma delimited list, or something else

/// <summary>
/// Set the default value of the specified property to the desired value if (and only if) the value is blank
/// or null.
/// </summary>
/// <param name="node">Current Content Node to update if needed</param>
/// <param name="propName">Property Name to set</param>
/// <param name="desiredDefaultValue">desired value (string) that the field should be set to</param>
private void SetDropDownListSingleValue(IContent node, string propName, string desiredDefaultValue)
{
  if (node.HasProperty(propName))
  {
    var currentValue = node.Properties[propName].Value;
    if (string.IsNullOrEmpty(DataUtilities.ObjectAsString(currentValue)))
    {
      var dtDefs = umbraco.library.GetPreValues(node.Properties[propName].PropertyType.DataTypeDefinitionId);
      dtDefs.MoveNext();

      foreach (XPathNavigator item in dtDefs.Current.SelectChildren("preValue", ""))
      {
        if (desiredDefaultValue.Equals(item.InnerXml, StringComparison.OrdinalIgnoreCase))
        {
          node.Properties[propName].Value = item.GetAttribute("id", "");
          break;
        }
      }

      ApplicationContext.Current.Services.ContentService.SaveAndPublishWithStatus(node);
    }
  }
}