The zero-width rect along the left edge of rect, spanning its full height. A pop-up placed
against it sits below (or above) all of rect, horizontally centered on its left edge.
Parameters
rect: DOMRect
The rect to take the left edge of, such as a selection's box from measureBox.
Returns DOMRect
A new rect at rect's left and top, with zero width and rect's height.
This export is unstable and may change shape or disappear without notice
The zero-width rect along the left edge of
rect, spanning its full height. A pop-up placed against it sits below (or above) all ofrect, horizontally centered on its left edge.