What
CSS-like viewport relative units that would work side-by-side with the the current units; percentage, px, points
-
vw - relative to the viewport’s width
-
vh - relative to the viewport’s height
Why
In many cases there’s going to be the need to size something relative to the screen estate. Although the current percentages (%) does a part of this, it does not replace the functionality of viewport relative units. It also allows for the width to be the same as the height - but still responsive.
Example
Square grid cells
<Grid ColumnCount="2">
<Rectangle Width="50vw" Height="50vw"/> <Rectangle Width="50vw" Height="50vw"/></Grid>