SVG className and href reflected as plain strings, so el.className.animVal
and el.href.animVal were undefined, which made new URL(svgEl.href.animVal)
throw and broke any SVG-aware script. Add an SVGAnimatedString class
(baseVal/animVal both read the live attribute; baseVal writable) and make
the className and href getters return it for SVG-namespace elements. href
falls back to the legacy xlink:href. HTML elements are unchanged.