Untested example of dealing with handled events and focused controls.

FocusedEventHandling.cs

const string controlName = "My text field";
string myString = "Text";


void OnGUI ()
{
	EventType handledEventType = Event.current.type;
	
	GUI.SetNextControlName (controlName);
	myString = GUILayout.TextField (myString);
	
	if (Event.current.alt && handledEventType == EventType.mouseDown && Event.current.type == EventType.used && GUI.GetNameOfFocusedControl () == controlName)
	{
		Debug.Log ("Alt-click handled with focused control being " + controlName);
	}
}