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By default the viewport is document.body
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Several browsers need to improve body's style by setting its width and height to 100%
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In this case a window will become movable on all the available document.body's space.
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Besides, there is no need for you to call any other methods that will affect the viewport.
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<input type="button" value="Open Demo" onclick="window.open('inc/01_default_demo.html');">