Can't call raycast on plane to get mouse position? Beginner Question

I’m trying to run the sample code from the API here: Unity - Scripting API: Plane.Raycast

But it doesn’t run. Why can’t I call .Raycast on the groundPlane?

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
	public Plane groundPlane;
	public Transform markerObject;
	void Update() {
		if (Input.GetMouseButtonDown(0)) {
			Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
			float rayDistance;
			if (groundPlane.Raycast(ray, out rayDistance))
				markerObject.position = ray.GetPoint(rayDistance);
			
		}
	}
}

Yields the following error:
Assets/Scripts/Player/old/ExampleClass.cs(11,41): error CS1061: Type Plane' does not contain a definition for Raycast’ and no extension method Raycast' of type Plane’ could be found (are you missing a using directive or an assembly reference?)

Some online tutorial code also yields a similar set of errors? For starters, when initializing the plane, I can’t pass the two parameters, when the API says I can?

Ray ray = viewCamera.ScreenPointToRay (Input.mousePosition);
		Plane groundPlane = new Plane (Vector3.up, Vector3.zero);
		float rayDistance;

		if (groundPlane.Raycast(ray,out rayDistance)) {
			Vector3 point = ray.GetPoint(rayDistance);
			Debug.DrawLine(ray.origin,point,Color.red);
			//Debug.DrawRay(ray.origin,ray.direction * 100,Color.red);
			controller.LookAt(point);
		}

Hmmm… I just checked, and the function does exist… and it should work with the code you’ve provided. Do you have any other scripts called “Plane” that may be conflicting?

Also, I note that the file you are editing is in: Assets/Scripts/Player/old/

Could that be a file you tried to deprecate?