PopupWidget is not correctly clipped with left/right edge (other ClippableElements work fine). This is because of the hardcoded 320px width (or any other explicit width) on the .oo-ui-popupWidget-popup ($clippableContainer), which is the parent element of .oo-ui-popupWidget-body ($clippable).

ClippableElement expects the container to adjust to the dimensions of the clippable, but since it has an explicit width it doesn't, and all hell breaks loose. We can't simply remove the width, because that will cause popups to become very narrow (as narrow as possible to render the text in them). I don't know how to solve this.

Note that this is rarely an issue, as PopupWidgets try to move themselves to the right/left if they would overlap the left/right edge. However in some cases it is not possible, e.g. for popups with position: 'before'/'after' or when the viewport is narrower than the popup.

LTR	RTL