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The translucent left column is the sidebar — the split-rectangle button toggles it

Sidebar (Source List)

/ NavigationSplitView · NSSplitViewController /

also called source list, navigation sidebar, split view sidebar

A sidebar is the leftmost navigation column used by apps such as Finder and Mail to organize destinations into sections. AppKit calls its list appearance a source list, while modern SwiftUI normally builds the structure with NavigationSplitView and sidebar list style. It can collapse independently of the main content and often uses a translucent material behind its rows.

If you called it…

“the translucent list down the left side of a mac app”“finder style navigation column”“left panel with sections and selected rows”“sidebar that collapses next to the main content”“list of folders or pages on the left”“mac navigation rail with a frosted background”

…you meant a sidebar (source list).

Anatomy — every part, named

1
Source-list styleNSTableView.Style.sourceList
The spacious, vibrancy-aware Finder-like treatment of the rows is AppKit's source-list style.
2
Section headerNSOutlineViewDelegate.outlineView(_:isGroupItem:)
The small emphasized label dividing destinations into groups such as Favorites or iCloud is a section header.
3
Selection pillNSTableRowView.isSelected
“The rounded colored background behind the current row” is the sidebar's selection pill.
4
Sidebar toggle toolbar buttonNSSplitViewController.toggleSidebar(_:)
The standard split-rectangle toolbar icon that reveals or hides the leading column is the sidebar toggle.

Prompt — paste into your agent

Build a macOS Sidebar (Source List) with NavigationSplitView (AppKit: NSSplitViewController), using the native translucent sidebar appearance and source-list row selection. It must occupy the left column, support collapsing, and keep navigation separate from the detail content.

Debug prompt — when it misbehaves

Paste this, then describe what you’re seeing — it hands your agent the classic failure modes to rule out first.

Debug my macOS sidebar (NSSplitViewController sidebar item, SwiftUI NavigationSplitView). Rule out: the frosted vibrancy missing because the sidebar content is not inside the sidebar-material effect view; toggleSidebar wired to the wrong split view item; the width not persisting without an autosaveName; the selection highlight losing its rounded inset style when the list style changes. The symptom:

In code

The exact names this thing goes by in code — each row is one framework’s word for it. Use the row that matches your project (or paste it into your prompt).

SwiftUI	`NavigationSplitView`
AppKit	`NSSplitViewController`
AppKit	`NSSplitViewItem(sidebarWithViewController:)`
AppKit	`NSTableView.Style.sourceList`	the standard AppKit list appearance
SwiftUI	`ListStyle.sidebar`

If you called it…

Anatomy — every part, named

Prompt — paste into your agent

Debug prompt — when it misbehaves

In code

See also

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