Masking shapes in HTML5 canvas?

Question

Apologies if this has been asked elsewhere but it's pretty hard to phrase as it is so I couldn't find anything.

Is there any way to implement masks in canvas?

For example, using shapes only (no images) I draw a house with a window. I also have a shape representing a person. I want that person to appear at the window - but obviously only so much as the window allows should be visible of the person. The rest would be masked.

I thought about emptying the part of the house occupied by the window, such that there was a genuine hole in the layer, which makes the problem easy to solve.

But I'm conscious you can't delete shapes or parts of shapes in canvas, only draw new stuff over old stuff. So in a multi-layered environment (I'm making a game in Kinetic.JS), what exactly can I do?

Sorry if any of this is poorly explained - new to the whole graphic thing.