The Overlays in the SVG are calculated via getBoxQuads and then drawn into an overlay layer
See the SVG Element and MathML Elemnts have a wrong overlay. They only works correctly in Firefox, when you
enable the
native getBoxQuads API. It's cause we display in a grid, so I don't know the offset in the control, and it
could not be calculated via getBoundingClientRect cause of the rotation.
This could be fixed if the browsers support offsetLeft & top for all elements, or natively support
getBoxQuads.
In the "Click Overlay" you see the clicked element in transformed coordinates.