Constructor restrictions for Custom Elements in Web Components

Question

In the W3C custom elements spec, it is mentioned that within the Custom element constructor:

The element must not gain any attributes or children, as this violates the expectations of consumers who use the createElement or createElementNS methods.

I am finding it difficult to understand what expectations are we violating. My initial guess was that using createElement to create a custom element does not invoke the Constructor behind the scenes, but that does not seem to be the case based on a proof of concept which I did.

Answer 1

Read the answers and comments from this one first:

• Attaching shadow DOM to a custom element removes error, but why?

Then these

• Failed to execute 'createElement' on 'Document': The result must not have children

• Deferred setAttribute call in Custom Element constructor causes DOM error. Is it a bug?