The document tabs allow you to navigate between the different elements opened in the different editors. Both the code and the UI appear in these tabs.
Hovering over a tab opens a preview thumbnail: window, report, query, code ....
The easiest way to close a document is by clicking the close icon in the tab. You can also click the mouse wheel: the hovered element is then closed.
Each tab has a context menu with several options. The "Close all but this" option is absolutely essential.
If the tabs overflow the available space, they become scrollable: simply use the mouse wheel to scroll through the different elements. You can also drag and drop tabs.
The list of all open elements can also be displayed in a menu.
Remark: The context menu of the open documents bar (not of an individual tab) allows you to open recently closed elements ("Recently closed" option).