Injection Scripts Executing Multiple Times

I've read the documentation and understand that this is to be expect开发者_Python百科ed:

Scripts are injected into the top-level page and any children with HTML sources, such as iframes. Do not assume that there is only one instance of your script per browser tab.

I'm wondering, though:

1. Other than iframes, what other elements have "HTML sources" (images? objects?)? The term "HTML sources" is uncomfortably vague to my ears.
2. Is there any way to detect which element is executing the script?

I've filtered out iframes by determining that window === window.top, as recommended, but other elements are still executing the script and it's executing a lot more than I'd like.

Thanks.

It's really my own fault that I'm answering my own question because I didn't really provide enough information in my question. In my defense, I didn't know at the time that I was providing too little information.

Anyway, while traveling down the road to a solution for this, I asked a question on Apple's dev forum and included the following bit of key info:

• Everything in the script occurs on the beforeload event of the document (or was supposed to).

What I learned was that the beforeload event only fires for subresources within the document. Not for the document (or window) itself. I removed the event handler and made sure that the script was applied as a start script (it was). I'd already applied the test for the window as top window so I was covered. Now my injection script only fires once.

Other HTML sources may be frames or object tags (with HTML contents). I don't think it can be anything else. However, to the extent of my knowledge, they should also be filtered off with window === window.top. Try console.loging the document.location variable to see which URL runs your injected script, and maybe you can find what loads them.