Currently, elem.attributes does not include the style attribute since that's stored as a separate object. See: https://github.com/developit/undom/blob/master/src/undom.js#L93-L95
This differs from my expectations. It also means that the provided serializeHtml() function doesn't include inline styles without modification.
Update: also, elem.style.cssText returns an object when a string is expected. Is this level of DOM compliance out-of-scope for undom or is this a reasonable expectation?