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Documentation: $mouse should be mouse?

In the builder documentation, at Mouse Component, it says that mouse x position can be obtained via
$mouse.getPos()[0]

I tried reproducing the steps in the documentation order to update the position of a polygon by entering the text below for Position [x,y]
($mouse.getPos()[0], $mouse.getPos()[1])

When I ran the experiment, I got the error
polygon.setPos(($mouse.getPos()[0], $mouse.getPos()[1]), log=False)

However, I did work out when I wrote:
(mouse.getPos()[0], mouse.getPos()[1])

PS - Same result for polygon size