as specified by [rsvg.handle.Handle.setSizeCallback].
Handle.ex
double ex() @propertyGet ex property.
Returns
Exact height, in pixels, of the rendered SVG before calling the size callback
Deprecated
Reading each of the size properties causes the size of the
SVG to be recomputed, so reading both the em and ex properties will cause two such computations. Please use [rsvg.handle.Handle.getIntrinsicDimensions] instead.