Possible mistake in docs

[passchn]

Hello!

When inserting an image in another, this will place the image in the center of the x-axis on the top and move it down by 15%/px or whatever:

$book->insert($image, 'top-center', 0, 15);

However, using top-center is not documented. Only center. Trying to move the image down with the fourth param y after using center as the second param does not work.