What it does

MD View becomes a side-by-side markdown viewer when you press Ctrl+Alt+S (or pick View → Open Split View). The first toggle creates an empty secondary slot and switches the active focus to it — the layout still looks single-pane, with the primary doc still visible. The next file you open (drag-and-drop, workspace tree click, or Ctrl+O) lands in that secondary slot, and that’s when the window actually splits into two panes. From there each pane has its own scroll position, its own navigation history (back/forward), its own fold state, and its own document context. Dragging the splitter resizes the panes; the ratio is remembered between sessions.

The active pane (the one you last clicked) is the one global overlays operate on — find, verify, copy-code, table-of-contents, lightbox, fullscreen toggle. A subtle accent border shows which pane is active so you always know.

Why it exists

A lot of reading work is comparison work. You’re reviewing a spec against an implementation. You’re reading the AI’s plan while looking at the file it’s planning to change. You’re cross-referencing two pieces of documentation. Tab-switching adds latency and breaks concentration; alt-tabbing between windows adds even more. Split view collapses the two-window pattern into a single window in your taskbar.

There’s a second use pattern: pinning a reference. Open the docs in the left pane, do your real work in the right, glance left when you need a reminder.

How to use it

Ctrl+Alt+S creates the secondary slot and shifts the active focus to it. The next file-open routes there: drop any file onto the window, click a file in the workspace sidebar, or hit Ctrl+O. To close split view, click the × on the secondary pane’s tab — the window snaps back to single-pane mode showing whatever was in the primary.

Under the hood

Split view is implemented in src/ui/split.js. It evolves the single-document store to a { primary, secondary } pair, with most of the rest of the codebase reading from a single state.activePane indirection. The watcher pipeline became a multi-path map (one debouncer per watched file path) and dispatches per-path events. Mermaid diagrams use per-pane render IDs so SVG IDs don’t collide between panes. Print and PDF export operate on the active pane only — exporting both panes simultaneously is out of scope for v1 (the output would always need a layout decision the user hadn’t made).

The active-pane indicator is a 2 px accent border on the active pane’s outer container — quiet enough not to be visual noise, distinct enough to read at a glance.

Use cases

• Spec vs implementation review: spec on the left, code-review markdown on the right.
• Two PRs at once: one PR’s description on the left, the other on the right; jump between them without losing context.
• Plan vs result: AI agent’s plan.md on the left, the actual output (or a review of it) on the right.
• Reading reference docs while taking notes: docs left, scratch.md right.
• Comparing two release notes: yours vs a competitor’s, two version bumps of the same project, etc.