Added this to knowledge base.

My comments:
hitest can find a collision between two movieclips or two points against a movieclip
Wrong. It can find collision between 1 point against movie clip.

var speed = 10
player._y += speed;
if (landscape.hitTest(player._x, player._y, true)) {
player._y -= speed;
}
Actually I find the example bad. There is no need to move movie clip, hittest and then move the movie clip back. Because you can use numbers instead of coordinates you should use it like this:
Code:
var speed = 10
if (!landscape.hitTest(player._x, player._y+speed, true)) {
	player._y += speed;
}
if (typeof enemy == "movieclip") {
I have never used typeof so I dont see much use for it. First of, I think it is bad idea to place anything other then enemy movie clips in enemyparent holder clip. But if you really must fill it useless junk, then hittesting with variable or function returns false anyway. Overall, I feel bringing typeof into the example only confuses the idea.

The above code assumes two movieclips have the names “circle1” and “circle2”.
The code also assumes graphics in both circles are centered into registration point. What if your circles have graphics aligned to the left?

You also should at least mention BitmapData.hitTest method which is different from the hittest you describe.