According to the [DOM spec](https://dom.spec.whatwg.org/#attr) attr.specified always returns `true`.

Therefore I think it's not necessary to use `getAttributeNode`:

> If result is null or undefined, or if it is an object, set the value of result to be the value of the AttributeNode obtained by calling getAttributeNode on element iff that AttributeNode is specified. That is, result is the equivalent of executing the following Ecmascript: var attr = element.getAttribute(name); var result = (attr && attr.specified) ? attr.value : null;

change into:

> If result is null or undefined, or if it is an object, set the value of result
 to be the value obtained by calling getAttribute(name) on element.

Also `name` may be in e.g. upper case at that step of the algorithm. I think it would be better to convert it to lower case at the first step of the algorithm and don't say that it should "match insensitively"