Add column selection for vertical multi-caret

Docs/Help/multi-caret.md

@@ -9,7 +9,8 @@ Place multiple carets in the document and type, delete, or press Enter at all of
 | **Ctrl+Click** | Toggle an additional caret at the clicked position. Click an existing additional caret to remove it. |
 | **Ctrl+Alt+↑** | Add a caret on the line above the topmost caret, at the sticky visual column (VS Code parity). |
 | **Ctrl+Alt+↓** | Add a caret on the line below the bottommost caret, at the sticky visual column (VS Code parity). |
-| **Alt + drag** | Build a vertical column of carets from the press row through the drag row at the press column (carets only). |
+| **Alt + drag** | Build a vertical column from the press row through the drag row. Zero horizontal extent creates carets; horizontal extent creates one selection per row. |
+| **Ctrl+Shift+Alt+↑/↓/←/→** | Create or extend a keyboard column selection. `PgUp` / `PgDn` extend by one viewport. |
 | **Escape** | Collapse back to the primary caret (clears all additional carets). |
 
 `Ctrl+Alt+↑/↓` track a *sticky visual column*: a short or tab-indented intervening line doesn't lose the column — the next long-enough line restores it. The chords are configurable per platform via `Editor.DefaultKeyBindings`; a terminal or window manager that grabs `Ctrl+Alt+arrow` is handled by remapping in config, not a separate built-in chord.
@@ -29,7 +30,7 @@ All edits are wrapped in a single `Document.RunUpdate` scope, so **Undo (Ctrl+Z)
 
 ## Visual feedback
 
-Additional carets are rendered as blinking, reverse-video cells by the `MultiCaretRenderer` (an `IOverlayRenderer`). The status bar in `ted` shows the total caret count when in multi-caret mode (e.g. "Ln 4, Col 1 (3 carets)").
+Additional carets are rendered as blinking, reverse-video cells by the `MultiCaretRenderer` (an `IOverlayRenderer`). Additional-caret selections render with the same active selection role as the primary selection. The status bar in `ted` shows the total caret count when in multi-caret mode (e.g. "Ln 4, Col 1 (3 carets)").
 
 ## Programmatic API
 
@@ -47,10 +48,19 @@ editor.ClearAdditionalCarets ();
 
 Additional carets are backed by `TextAnchor` instances, so they track insertions and deletions elsewhere in the document automatically (same mechanism as the primary caret).
 
+## VS Code parity and intentional deviations
+
+Column selection matches VS Code behavior: typing over a ranged column replaces each row's selection in one undo step; short rows clamp to the real line end without writing padding; dragging left of the anchor reverses the selection direction; `Esc` or a plain click collapses back to the primary caret.
+
+Intentional deviations:
+
+- **D1 — mouse modifier**: VS Code starts column selection with `Shift+Alt`+drag; this editor uses **`Alt`+drag** because Windows Terminal and xterm-family terminals reserve `Shift`+drag for terminal-side forced/block selection while an app has mouse mode enabled. Configurable mouse modifiers are tracked by [gui-cs/Terminal.Gui#4888](https://github.com/gui-cs/Terminal.Gui/issues/4888).
+- **D2 — add caret at click**: VS Code uses `Alt`+Click; this editor keeps the existing **`Ctrl`+Click** binding. `Alt` is the column-drag modifier, so an `Alt`+Click alias would need drag-threshold disambiguation.
+- **D3 — keyboard column-select**: not a deviation. `Ctrl+Shift+Alt+Arrow` and `Ctrl+Shift+Alt+PgUp/PgDn` match VS Code behavior when the terminal delivers the chord (TG's Kitty keyboard protocol support makes this available on capable terminals).
+- **D4 — sticky Column Selection Mode**: VS Code's modal toggle is out of scope; this editor implements the drag and keyboard gestures, not a persistent mode with menu/status UI.
+- **D5 — multi-cursor paste distribution**: VS Code can distribute N clipboard lines over N cursors. This is deferred as a separate follow-up; typing and one-line paste replacement are covered here.
+
 ## Limitations (current alpha)
 
-- Selection is not yet per-caret; only the primary caret carries a selection.
 - Find/Replace operates on the primary caret only.
-- `Alt`+drag produces a column of *carets*, not a column *selection*. To replace a column, drag to place the carets, then `Shift+→`/`←` to grow each caret's selection, then type. Per-row column selection during the drag is the planned follow-up.
-- The column-drag modifier is `Alt`, not VS Code's `Shift+Alt`: terminals reserve `Shift`+drag for their own forced/block text selection while an app reads the mouse, so `Shift+Alt`+drag never reaches the editor. Making the mouse modifier user-configurable (to opt back into `Shift+Alt`) is tracked by [gui-cs/Terminal.Gui#4888](https://github.com/gui-cs/Terminal.Gui/issues/4888).
 - Toggling Word Wrap while a vertical block is live dismisses the block.

examples/ted/TedApp.cs

@@ -142,33 +142,34 @@ public TedApp (bool readOnly = false, string? configPath = null)
             }
         };
         ShowTabsCheckBox.Value = Editor.ShowTabs ? CheckState.Checked : CheckState.UnChecked;
-        PreviewCheckBox.ValueChanged += (_, e) =>
-        {
-            ToggleMarkdownPreview ();
-            _previewMarkdownMenuItem.Title = ToggleTitle (e.NewValue == CheckState.Checked, "_Preview Markdown");
-        };
+        OverwriteShortcut = new Shortcut (Key.Empty, "INS", null) { MouseHighlightStates = MouseState.None };
+        LocShortcut = new Shortcut (Key.Empty, FormatLoc (1, 1), null) { MouseHighlightStates = MouseState.None };
         LoadStatusSpinner = new SpinnerView
         {
             Style = new SpinnerStyle.Aesthetic (),
             Width = 8,
             AutoSpin = false,
             Visible = false
         };
+        LoadSpinnerShortcut = new Shortcut
+        {
+            CommandView = LoadStatusSpinner,
+            Title = string.Empty,
+            MouseHighlightStates = MouseState.None
+        };
+        PreviewCheckBox.ValueChanged += (_, e) =>
+        {
+            ToggleMarkdownPreview ();
+            _previewMarkdownMenuItem.Title = ToggleTitle (e.NewValue == CheckState.Checked, "_Preview Markdown");
+        };
 
         StatusBar statusBar =
             new ([
                 new Shortcut { Title = "Language", CommandView = LanguageShortcut },
                 new Shortcut { Title = "Theme", CommandView = ThemeDropDown },
-                LoadSpinnerShortcut = new Shortcut
-                {
-                    CommandView = LoadStatusSpinner,
-                    Title = string.Empty,
-                    MouseHighlightStates = MouseState.None
-                },
-                OverwriteShortcut = new Shortcut (Key.Empty, "INS", null)
-                    { MouseHighlightStates = MouseState.None },
-                LocShortcut = new Shortcut (Key.Empty, FormatLoc (1, 1), null)
-                    { MouseHighlightStates = MouseState.None }
+                LoadSpinnerShortcut,
+                OverwriteShortcut,
+                LocShortcut
             ])
             {
                 AlignmentModes = AlignmentModes.IgnoreFirstOrLast

specs/multi-caret/spec.md

@@ -55,7 +55,7 @@ Add multi-caret support to the Editor. Expose `IReadOnlyList<int> AdditionalCare
 
 ## Out of Scope
 
-- Column/block selection mode — the "multi-select" follow-up PR. **When built, it must also close the carried-forward selection-preservation gap:** multi-caret `Tab`/`Shift+Tab` block-indent must preserve the primary *and* per-caret selections (parity with the single-caret `IndentSelectedLines` path; today `ClearAdditionalCaretSelections ()` collapses them post-edit). See `specs/vertical-multi-caret/spec.md` § Out of Scope → *Column / box selection* for the full requirement.
+- Sticky Column Selection Mode — VS Code's modal toggle where ordinary clicks/arrows keep column-select behavior until disabled. The drag and keyboard column-selection gestures are in scope for `specs/vertical-multi-caret/spec.md`; the persistent mode with menu/status UI is a separate follow-up.
 - Multi-caret find/replace
 
 ## Notes

specs/overwrite-mode/spec.md

@@ -1,7 +1,7 @@
 # Overwrite (Insert-Replace) Mode
 
-**Status**: Implemented  
-**Issue**: [#146](https://github.com/gui-cs/Editor/issues/146)  
+**Status**: Implemented
+**Issue**: [#146](https://github.com/gui-cs/Editor/issues/146)
 **Updated**: 2026-05-17
 
 ## Summary

specs/public-api.md

@@ -36,10 +36,9 @@ public class Editor : View
     public void ToggleCaretAt (int offset);                       // multi-caret (Ctrl+Click toggle)
     public void ClearAdditionalCarets ();                         // multi-caret (Esc collapse)
     // vertical-multi-caret adds NO new public API: Ctrl+Alt+CursorUp / Ctrl+Alt+CursorDown
-    //   create a vertically-aligned column of carets at the sticky visual column, and
-    //   Alt + LeftButton drag builds a column of carets (carets only). Both reuse the
-    //   existing AdditionalCaretOffsets / HasMultipleCarets / ClearAdditionalCarets surface and
-    //   are bound through the configurable Editor.DefaultKeyBindings ([ConfigurationProperty]).
+    //   create a vertically-aligned column of carets at the sticky visual column; Alt + LeftButton
+    //   drag and Ctrl+Shift+Alt+Arrow/Page create column selections. All reuse the existing
+    //   AdditionalCaretOffsets / HasMultipleCarets / ClearAdditionalCarets surface.
 
     // --- Display ---
     public bool ShowLineNumbers { get; set; }                     // exists
@@ -157,5 +156,6 @@ public readonly record struct TextDocumentProgress (
 | 2026-05-11 | ReadOnly property landed on Editor | read-only |
 | 2026-05-12 | `ISearchStrategy?` `SearchStrategy { get; set; }` landed on Editor; string-based FindNext/FindPrevious/ReplaceNext/ReplaceAll overloads retained as convenience wrappers | find-and-replace |
 | 2026-05-16 | Vertical multi-caret keybindings (`Ctrl+Alt+CursorUp/Down`, `Alt+Drag`) added via `Editor.DefaultKeyBindings`; no new public Editor API (R8) | vertical-multi-caret |
+| 2026-05-17 | Column selection during `Alt+Drag` and `Ctrl+Shift+Alt+Arrow/Page` added without new public Editor API | vertical-multi-caret |
 | 2026-05-17 | Streaming `TextDocument.LoadAsync` / `TextDocument.SaveAsync`, `TextDocumentProgress`, `TextDocument.Encoding`, and delegating `Editor.LoadAsync` / `Editor.SaveAsync` landed | file-io |
 | 2026-05-17 | `Editor` implements `IDesignable`; `EnableForDesign()` seeds C# sample code with syntax highlighting and line numbers | design-time |

specs/textview-parity-gap/spec.md

@@ -58,7 +58,7 @@ exposed today.
 
 ### 2. Overwrite / insert-replace mode → [#146](https://github.com/gui-cs/Editor/issues/146)
 
-**TextView**: `Used` flag + `Command.ToggleOverwrite` (Insert key), `Command.EnableOverwrite`,
+**TextView**: overwrite-mode state + `Command.ToggleOverwrite` (Insert key), `Command.EnableOverwrite`,
 `Command.DisableOverwrite`; a distinct caret rendering for overwrite; typing replaces the rune
 under the caret instead of inserting.