实现
factory SvgElement.svg(String svg,
{NodeValidator? validator, NodeTreeSanitizer? treeSanitizer}) {
if (validator == null && treeSanitizer == null) {
validator = new NodeValidatorBuilder.common()..allowSvg();
}
final match = _START_TAG_REGEXP.firstMatch(svg);
Element parentElement;
if (match != null && match.group(1)!.toLowerCase() == 'svg') {
parentElement = document.body!;
} else {
parentElement = new SvgSvgElement();
}
var fragment = parentElement.createFragment(svg,
validator: validator, treeSanitizer: treeSanitizer);
return fragment.nodes.where((e) => e is SvgElement).single as SvgElement;
}