"Files that just close": Ironically, VSCode adopted that feature from Sublime, and it works exactly the same. They're "preview" tabs, which you can recognize by

"Files that just close": Ironically, VSCode adopted that feature from Sublime, and it works exactly the same. They're "preview" tabs, which you can recognize by the fact that the title is rendered in italics. You can make the tab permanent either by editing the file, or by hitting Cmd-K-E (on macOS, no idea about other OSes).