setAttributeNS 方法
实现
@pragma('dart2js:tryInline')
void setAttributeNS(String? namespaceURI, String name, Object value) {
// TODO(41258): Delete these assertions after forcing strong mode.
// Protect [name] against string conversion to "null" or "undefined".
assert(name != null, 'Attribute name cannot be null');
// TODO(sra): assert(value != null, 'Attribute value cannot be null.');
_setAttributeNS(namespaceURI, name, value);
}