A cloned window is the exact same document in a new tab window. You can open as many clones as you want. They can be opened in the same view or to the right/left.
Cloning is very similar to "Split window" and allow you to edit several part of the same document using different windows.
Open the tab context menu and select "Open clone..." or "Open clone to the right...".
Here we have the same document opened to the left and right view allowing us to edit several places in the same document.