This I didn't even know. I checked it and yes it works.
A long press on text marks it with a blue border. This is copied to the clipboard.

I don't quite understand what you mean with slide right.
If I tap the text within the blue border the text is shown in a separate window which comes from the right ( I guess you mean this).
When I highlight a word or a sentence from the text in this window and press Copy, it does not copy the highlighted part to clipboard every time (saw it working just now but only once).

Edit: Tried it a few times. The Copy button only works the first time you use it during a session. The times after that it doesn't work and you can only paste the result of the first initial copy action.