The tree mirrors your folders exactly, to whatever depth they go, with the file's own name on each document so you can find it again anywhere else.
Every folder opens and closes on its own arrow; Enter or Space works it from the keyboard.
Each folder carries a count of what it holds, so a shut branch tells you whether it is worth opening.
Folders named venv and node_modules are hidden by default, since what they hold is somebody else's code. So are documents with nothing to read: a blank text file, a Markdown file declaring fields with no body beneath them, a web page that is nothing but scripts and markup, a Word document with no words in it. A folder left with nothing to read goes with them.
One button at the right end of the bottom tray shows them all again. Its picture shows the filter as it stands, crossed out while everything is shown; the choice is remembered. A PDF is never hidden this way, since knowing would mean extracting it; a file opened on its own is never filtered.
Folders you leave open are remembered, so a run opens as the last one closed.
Everything opens shut and nothing is selected until you select it. A reader who has chosen nothing is not shown something chosen for them.
Reading one
The selected document is rendered to be read, not shown as raw text.
Plain text is shown exactly as it was typed, since its line breaks are the author's own layout rather than the renderer's.
The fields it declares are laid out plainly; an oversized field gets a heading of its own after the body rather than crowding the top.
A document that cannot be read is still listed, with the reason shown in the pane rather than raised as a dialog.
The text column is held to a readable line length, so a wide window gives margins rather than longer lines. What that caps is where a line wraps rather than how much of the window a page may use.
A block of code or a diagram is drawn as one box, in a face whose box characters draw whole strokes, so a diagram joins up rather than arriving as dashed lines. Too wide to wrap, it keeps every pixel the window has and scrolls sideways only once the window is genuinely too narrow for it.
The page reads itself gently down and hands control straight back the moment you scroll.
The foot of the window says what you have open and how much of it there is: the kind of document at the left, its characters and its lines at the right, the way an editor's status bar says it.
That count is of the text you are reading rather than of the bytes of the file, so a Markdown document is counted beneath the fields it declares while a PDF or a Word document is counted as what was read out of it. A document that could not be read still names its kind, which comes from the file name, while carrying no count, which would need the text.