…tributes`

Using this flag previously read attributes in the element constructor (in addition to patching setAttribute). This covers use cases except imperative or parser created custom elements (not upgraded). In that case the element will not have attributes in the constructor. This is addressed here by checking if the element has a parentNode (which will also not be true in these cases) and if so, records attributes at connected time. This is not always done to avoid having to filter out changes made by bindings.

…-imperative-attributes