Multiple GUILayoutOption for one GuiLayout.TextArea?

This fails:

var TextAreaLayoutOptions : UnityEngine.GUILayoutOption
 = GUILayout.Height(200) + GUILayout.ExpandHeight(false);

GUILayout.TextArea(someText, TextAreaLayoutOptions);

What is the concat operator for two GUILayoutOption?

There isn't a concat operator. You can either pass an array of GUILayoutOptions or pass several of them directly to the function. For example:-

GUILayout.TextArea(someText, GUILayout.Height(200), GUILayout.ExpandHeight(false));