MDN URL

https://developer.mozilla.org/en-US/docs/Web/API/Element/securitypolicyviolation_event

What specific section or headline is this issue about?

No response

What information was incorrect, unhelpful, or incomplete?

You should add the handler for this event to a top level object (i.e. {{domxref("Window")}} or {{domxref("Document")}}).
While the property exists in HTML elements, you can't assign a handler to the property until the elements have been loaded, by which time this event will already have fired.

What did you expect to see?

This paragraph rephrased, to something similar to:

You should generally add the handler for this event to a top level object (i.e. listen for the {{domxref("Document.securitypolicyviolation_event", "securitypolicyviolation")}} event on {{domxref("Document")}} instead).
While the event may originate from HTML elements, JavaScript that assigns a handler to the element usually executes after the element has been loaded, by which time this event has already fired.
You can only successfully listen to this event if the loading starts after the listener is attached, usually by dynamically modifying the fetch target via JavaScript.

And, later, the example should demonstrate a dynamically constructed element.

const img = document.createElement("img");
img.onsecuritypolicyviolation = console.log;
img.src = "https://..."; // Fetching starts here, which is after the handler is attached

Do you have any supporting links, references, or citations?

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Do you have anything more you want to share?

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