[SVG] baseval.value of an SVG element nested inside a symbol returns an error

[Karl Dubost]

https://codepen.io/webcompat/pen/Jjzpogz

  <svg>
    <symbol>
      <g>
        <rect id="r1" width="20%" height="30%" />
      </g>
    </symbol>
  </svg>


the width of the rect returns:

Safari:
=======================================
width.baseVal.valueAsString: 20%
width.baseVal.valueInSpecifiedUnits: 20
=======================================
with an error message in the console:
NotSupportedError: The operation is not supported.


Firefox:
=======================================
width.baseVal.valueAsString: 20%
width.baseVal.valueInSpecifiedUnits: 20
width.baseVal.value: 60
=======================================


If you remove the symbol element, it returns the correct result:
Safari:
=======================================
width.baseVal.valueAsString: 20%
width.baseVal.valueInSpecifiedUnits: 20
width.baseVal.value: 60
=======================================


Because of this, WebKit fails
https://wpt.fyi/results/svg/geometry/svg-baseval-in-display-none.html

[Radar WebKit Bug Importer]

<rdar://problem/121912972>