Shape Builder: a Shift-drag draws a marquee and merges every region it reaches

A Shape Builder drag merged only the regions the pointer passed over,
and the tool did not read Shift. The reference app's Shape Builder page
describes a Shift-drag that draws a rectangular marquee to merge many
paths at once.

With Shift held at the press, the drag now draws a rectangular marquee
from where it started to the pointer. The regions it reaches are shaded
while it is drawn and merge into one shape on release; with Alt also
held at the press, they are deleted. The marquee reaches each region
whose outline crosses it or has an anchor inside it, and the region that
holds the whole marquee. A Shift-click that does not move is a click,
and a drag without Shift works as before. With In Merge Mode, Clicking
Stroke Splits the Path on, a Shift-click on a stroke splits it as a
click does; a marquee splits no stroke, and while it is drawn the
pointer does not show scissors and no stroke is highlighted.

shapeBuilder.merge takes the marquee as rect: [x, y, width, height],
where x and y are where the drag started, and points may then be left
out. For Pick Color From Artwork, the corner where the drag started
counts as the drag's first point, and the opposite corner counts as its
last. With rect, splitStroke does not split a stroke.

Docs: docs/mcp.md, docs/target-app-parity.md.

docs/mcp.md

@@ -4590,6 +4590,23 @@ With `pickColorFrom` `swatches`, the run takes the current fill as its stroke. T
 {"name":"run_command","arguments":{"command":"shapeBuilder.merge","params":{"points":[[50,-1]],"splitStroke":true}}}
 ```
 
+With Shift held at the press, a Shape Builder drag draws a rectangular marquee from where the drag started to the
+pointer, and the Selection option does not apply to it. The regions the marquee reaches are shaded while it is drawn
+and merge into one shape on release; with Alt also held at the press, they are deleted. The marquee reaches a region
+when the region's outline crosses the rectangle or has an anchor inside it, or when the region holds the whole
+rectangle. The tool sends the marquee to `shapeBuilder.merge` as `rect: [x, y, width, height]` in place of `points`:
+`x` and `y` are where the drag started, and the width and height are negative for a drag up or to the left. For Pick
+Color From Artwork, the corner where the drag started counts as the drag's first point, and the opposite corner counts
+as its last: the merged shape takes the look of the front-most selected object under the first corner, else of the one
+under the opposite corner, else of the front-most selected object. A Shift-click that does not move sends `points`
+as a click does, so with `clickStrokeSplitsPath` on, a Shift-click on a stroke splits it. A marquee splits no stroke,
+however little the pointer moves: the tool sends no `splitStroke` with `rect`, and `shapeBuilder.merge` does not split
+a stroke when it has `rect`. With both `rect` and `points`, the command also touches what the points touch.
+
+```json
+{"name":"run_command","arguments":{"command":"shapeBuilder.merge","params":{"rect":[50,50,200,200]}}}
+```
+
 ## Perspective grid
 
 The grid is document data (`perspective.grid.set` edits the model directly). `perspective.grid.get` reads it:

docs/target-app-parity.md

@@ -659,6 +659,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
     With Pick Color From Artwork, a merged shape takes the appearance, opacity and blending mode of the object where the drag starts, else of the object where it ends, else of the front-most selected object, as the [Shape Builder combine page](https://web.archive.org/web/20251006211643/https://helpx.adobe.com/illustrator/desktop/draw-shapes-and-paths/draw-shapes/combine-shapes-with-shape-builder-tool.html) states ("The art style of the object where the mouse drag was initiated is applied to the merging shapes"). A click in an area that no selected object covers, such as a hole other shapes enclose, takes the front-most selected object's look (`shapeBuilder.merge` `points`: the first point is where the drag starts, and the last point is where it ends).
     Double-clicking the Shape Builder tool opens Shape Builder Tool Options ([Shape Builder tool options](https://web.archive.org/web/20260105172244/https://helpx.adobe.com/illustrator/using/building-new-shapes-using-shape.html)): with Consider Open Filled Paths as Closed off, a filled open path cuts regions as an unfilled one does; Pick Color From Color Swatches fills merged shapes with the current fill, the Left and Right arrow keys step it through the document's color swatches, and Cursor Swatch Preview shows the current fill and the swatches before and after it above the pointer; Selection Straight Line merges what the line from a drag's first point to its last crosses ([Setting Illustrator's Shape Builder Options](https://web.archive.org/web/20260615204453/https://creativepro.com/setting-illustrators-shape-builder-options/)); with Highlight Fill off, merge mode shades no regions (`shapeBuilder.merge` `openFilledAsClosed` and `pickColorFrom`).
     With In Merge Mode, Clicking Stroke Splits the Path on in the same dialog, a click on a stroke in merge mode splits its path into the run of stroke under the pointer and the rest of the path, as the [Shape Builder tool options](https://web.archive.org/web/20260105172244/https://helpx.adobe.com/illustrator/using/building-new-shapes-using-shape.html) page describes; the run goes from the anchor or crossing point before the pointer to the one after it, and the pointer shows scissors over it. Highlight Stroke When Editable draws that run in the color chosen in its Color list (Red by default), and with Pick Color From Color Swatches the run takes the current fill as its stroke (`shapeBuilder.merge` `splitStroke`).
+    A Shift-drag with the Shape Builder tool draws a rectangular marquee for merging many paths at once, as [Combine shapes with the Shape Builder tool](https://web.archive.org/web/20251006211643/https://helpx.adobe.com/illustrator/desktop/draw-shapes-and-paths/draw-shapes/combine-shapes-with-shape-builder-tool.html) describes: the regions it reaches are shaded while it is drawn and merge into one shape on release, or with Alt they are deleted. The marquee reaches each region whose outline crosses it or has an anchor inside it, and the region that holds the whole marquee; this rule is VectorCraft's own. For Pick Color From Artwork, the marquee's starting corner is where the drag starts and the opposite corner is where it ends (`shapeBuilder.merge` `rect`).
     The Blob Brush Tool Options have Keep selected and Merge only with selection, both off by default: while Keep selected is off, the blob a stroke draws or merges into is not selected afterwards, and while Merge only with selection is on, a stroke merges only with selected blobs of its color that it touches (`path.blob` `keepSelected` and `mergeOnlySelection`).
 - **Ruler guides as layer objects:** a guide goes on the current layer, shows, hides, locks and is deleted with it, is listed in the Layers panel (its row selects it) and moves to another layer (`guide.setLayer`, or its row dragged onto that layer's rows); guides on a hidden or locked layer can't be selected, moved or deleted, Duplicate copies a layer's guides and Merge Selected and Flatten Artwork keep them on the merged layer; guides from files saved before guides had layers go on the top visible, unlocked layer when the document opens. Not done: guides stacked among the art of their layer (they are listed above it), a guide row's own eye and lock. Lock Guides also locks the objects made into guides: they can't be selected, moved or deleted (#1543); they are drawn in the guide colour and style of Preferences, and a dragged selection snaps to ruler guides with Smart Guides on (#1583, fixes #1534). The Transform panel shows a selected ruler guide's X or Y, and typing a value moves it (#1659, part of #1597). This is not established by the documentation we could find: the public help pages on guides, rulers and the Transform, Control and Properties panels (read again on 2026-10-14) describe selecting and dragging unlocked guides and the panels' X and Y for a selection, not a guide's position in a panel, and the one public statement of it is a user's [community answer](https://community.adobe.com/questions-652/adding-a-new-custom-guide-785586), which is not documentation. It is kept as a convenience pending the owner's decision, with no parity claim and nothing counted towards a score.
 - **Releasing ruler guides:** View › Guides › Release Guides turns the selected ruler guides into paths with no fill or stroke. An artboard guide becomes a line across its artboard, and a canvas guide becomes a line across the artboards (`view.guides.release {index?, ids?}`). A Cmd/Ctrl+Shift double-click with the Selection, Direct Selection or Group Selection tool releases the ruler guide or guide path under the pointer.