public object Item( 
   string fieldName
) {get; set;}

// Updates the "Description" attribute of the selected features in the specified selection set.
{
  // get the first layer and its corresponding selected feature OIDs
  var firstSelectionSet = selectedFeatures.ToDictionary().First();
  // create an instance of the inspector class
  var inspector = new Inspector();
  // load the selected features into the inspector using a list of object IDs
  await inspector.LoadAsync(firstSelectionSet.Key, firstSelectionSet.Value);
  // assign the new attribute value to the field "Description"
  // if more than one features are loaded, the change applies to all features
  inspector["Description"] = "The new value.";
  // apply the changes as an edit operation 
  await inspector.ApplyAsync();
}