What's the easiest way to copy the URL of a traditional HTML frame in Safari? As much as I hate HTML frames, a vendor uses a documentation platform that makes heavy use of them. Whenever I search for a documentation page, it displays in a frame, and I would like to be able to copy the URL of that page inside the frame to share with colleagues.

I would have expected to be able to do this by right-clicking on the frame and choosing "Copy Frame URL" or something, but that's not an option. At present I have to find the link to the page in question in a list of documentation contents, and copy that.
This is a little indirect however based on your example, right-click in the frame and select Open Frame in New Tab, then select the new Tab and copy the URL from the Address bar.