Does copy-paste text carry any metadata other than the text itself?

Yes, all the formatting info etc. is copied along with the text.

If want to paste the text only, you can use control-shift-V to paste without the formatting etc. in most programs.

In others such as Word, right-click and you will see a line with Paste options - one of which is the text only, without formatting.

You have to realize that webpages have full access to your clipboard, while formatting DOES get copied, the URL doesn't, but a webpage might muck with your clipboard to add on additional information.

Nice tip Robert

Yes. For example, if you copy from the edit page of a word processor such as Word, there is a lot of extra data copied that you don't see. A simple way to clear it is to paste into a simple text editor (e.g., Notepad) and then copy from there.