diff --git a/app/layout/SplitTree.zig b/app/layout/SplitTree.zig
index bcb8b86f6..78fa33e27 100644
--- a/app/layout/SplitTree.zig
+++ b/app/layout/SplitTree.zig
@@ -6,8 +6,10 @@
 //! picker fills them. Closing an empty leaf collapses the branch.
 const std = @import("std");
 const dvui = @import("dvui");
+const core = @import("core");
 
-pub const Side = enum { left, right, top, bottom };
+/// The docking widget's side: a pane tree and a place tree name an edge the same way.
+pub const Side = core.widgets.DockLayout.Side;
 
 pub fn axisOf(side: Side) dvui.enums.Direction {
     return switch (side) {
diff --git a/app/layout/State.zig b/app/layout/State.zig
index 46aa109cf..243029465 100644
--- a/app/layout/State.zig
+++ b/app/layout/State.zig
@@ -38,6 +38,14 @@ pub const StoreOffer = struct {
     title: []const u8,
 };
 
+/// An app's answer to where an open beside splits a place (`beside`).
+pub const Beside = struct {
+    ctx: *anyopaque,
+    /// The edge of place `name` an open beside splits, or null where it joins a place, becomes a
+    /// card, or `name` holds no documents.
+    edge: *const fn (ctx: *anyopaque, name: []const u8) ?SplitTree.Side,
+};
+
 /// How an application gives a document a home outside the slots its plugins made: a view of its
 /// own that holds documents (fizzy's workspaces). With one, a document carried in the view drag
 /// lands in any place as a view would, inside a new such view (`ViewDrag.place`).
@@ -169,10 +177,11 @@ tree_cleared: bool = false,
 slide_open: []const u8 = "",
 /// A place's view being dragged to another place. Empty `name` when idle.
 view_drag: ViewDrag = .{},
-/// The edge an open beside splits the documents' place on right now, set each frame by the app
-/// while a demo plays: that edge's drop zone is also published as the anchor `drop:beside`, so a
-/// tape aims at the place's answer, not at an edge it chose when it was written.
-beside: ?SplitTree.Side = null,
+/// Set each frame by the app while a demo plays: asked for each place a drag may land in, it
+/// names the edge an open beside splits that place on. That edge's drop zone is also published as
+/// the anchor `drop:beside`, so a tape aims at the target place's own answer, not at an edge it
+/// chose when it was written.
+beside: ?Beside = null,
 /// Floats are OS windows of their own (the application says so each frame, where it has them): a
 /// view let go over no window of the app's opens one there (`ViewDrag.apply`).
 floats_windowed: bool = false,
diff --git a/app/layout/ViewDrag.zig b/app/layout/ViewDrag.zig
index ce83ef85d..73e449dc8 100644
--- a/app/layout/ViewDrag.zig
+++ b/app/layout/ViewDrag.zig
@@ -1323,18 +1323,21 @@ pub fn drawZones(l: *Layout, name: []const u8, key: dvui.Id) void {
     // is the target, so a demo aims at the bubble rather than an offset from the place's middle.
     // Marked only while a tape asks for anchors, and ahead of the offer queue's limit (which has
     // nothing to do with the bubble being there).
-    if (target and !covered and core.anchor.wanted()) for (DropZones.all) |z| {
-        if (z == .remove and !zones.remove) continue;
-        const b = zones.bubble(z);
-        const r: dvui.Rect.Physical = .{ .x = b.c.x - b.r, .y = b.c.y - b.r, .w = 2 * b.r, .h = 2 * b.r };
-        switch (z) {
-            .edge => |side| {
-                core.anchor.markRect(key, r, true, "drop:{t}", .{side});
-                if (l.state.beside) |aimed_side| if (std.mem.eql(u8, @tagName(aimed_side), @tagName(side))) core.anchor.markRect(key, r, true, "drop:beside", .{});
-            },
-            else => core.anchor.markRect(key, r, true, "drop:{t}", .{z}),
+    if (target and !covered and core.anchor.wanted()) {
+        const beside = if (l.state.beside) |aim_at| aim_at.edge(aim_at.ctx, name) else null;
+        for (DropZones.all) |z| {
+            if (z == .remove and !zones.remove) continue;
+            const b = zones.bubble(z);
+            const r: dvui.Rect.Physical = .{ .x = b.c.x - b.r, .y = b.c.y - b.r, .w = 2 * b.r, .h = 2 * b.r };
+            switch (z) {
+                .edge => |side| {
+                    core.anchor.markRect(key, r, true, "drop:{t}", .{side});
+                    if (beside == side) core.anchor.markRect(key, r, true, "drop:beside", .{});
+                },
+                else => core.anchor.markRect(key, r, true, "drop:{t}", .{z}),
+            }
         }
-    };
+    }
     // Queued, not drawn: over everything, once every place has drawn (`drawOverlay`).
     const now = dvui.currentWindow().frame_time_ns;
     if (d.pending_frame != now) {
diff --git a/core/widgets/DropZones.zig b/core/widgets/DropZones.zig
index 0db908e0e..a66ecc084 100644
--- a/core/widgets/DropZones.zig
+++ b/core/widgets/DropZones.zig
@@ -48,7 +48,7 @@ const motion = @import("glass").motion;
 const liquid_glass = @import("glass").liquid_glass;
 const LiquidField = @import("glass").LiquidField;
 
-pub const Side = enum { left, right, top, bottom };
+pub const Side = @import("DockingWidget/Layout.zig").Side;
 
 pub const Zone = union(enum) {
     /// Into the place itself: a trade for a place that shows one view, a new tab for one that
diff --git a/plugins/workbench/src/Workbench.zig b/plugins/workbench/src/Workbench.zig
index ea3ce2a27..e9848c5a6 100644
--- a/plugins/workbench/src/Workbench.zig
+++ b/plugins/workbench/src/Workbench.zig
@@ -233,27 +233,26 @@ pub fn sideBeside(self: *const Workbench, anchor: u64) Panes.Side {
 /// What opening beside the person's pane asks of `core.placement.place`: the other pane that is
 /// there, if any, and the answer over the person's room and that pane's. Null before the person's
 /// pane has drawn, with no room to judge.
-const Beside = struct { other: ?u64, answer: ?core.placement.Result };
+const Beside = struct { other: ?u64, room: ?core.placement.Size, answer: ?core.placement.Result };
 
-fn besideAnswer(self: *Workbench) Beside {
-    const here = self.open_workspace_grouping;
+fn besideAnswer(self: *Workbench, here: u64) Beside {
     const other = for (self.workspaces.values()) |ws| {
         if (ws.grouping != here and !self.paneClosing(ws.grouping)) break ws.grouping;
     } else null;
-    const room = self.paneSize(here) orelse return .{ .other = other, .answer = null };
+    const room = self.paneSize(here) orelse return .{ .other = other, .room = null, .answer = null };
     var others: [1]core.placement.Size = undefined;
     const places: []const core.placement.Size = if (other) |g| blk: {
         others[0] = self.paneSize(g) orelse .{ .w = 0, .h = 0 };
         break :blk &others;
     } else &.{};
-    return .{ .other = other, .answer = core.placement.place(room, places) };
+    return .{ .other = other, .room = room, .answer = core.placement.place(room, places) };
 }
 
 /// The grouping a document opened beside the person's goes in (`core.placement.place`): another
 /// pane that is there, else a new one when the person's has room for two, else the person's own,
 /// where it becomes a card. The caller makes it the front card, as a plain open does.
 pub fn besideGrouping(self: *Workbench) u64 {
-    const asked = self.besideAnswer();
+    const asked = self.besideAnswer(self.open_workspace_grouping);
     // Not drawn yet, so no room to judge: beside as before, in the other pane if there is one.
     const answer = asked.answer orelse return asked.other orelse self.newGroupingID();
     return switch (answer) {
@@ -263,11 +262,12 @@ pub fn besideGrouping(self: *Workbench) u64 {
     };
 }
 
-/// The edge of the person's pane an open beside splits it on, or null where it joins a pane or
-/// becomes a card. What a demo's `drop:beside` aims at.
-pub fn besideEdge(self: *Workbench) ?Panes.Side {
-    const room = self.paneSize(self.open_workspace_grouping) orelse return null;
-    return switch (self.besideAnswer().answer orelse return null) {
+/// The edge of `grouping`'s pane an open beside it splits on, or null where it joins a pane or
+/// becomes a card. What a demo's `drop:beside` aims at, over the pane it is aimed at.
+pub fn besideEdge(self: *Workbench, grouping: u64) ?Panes.Side {
+    const asked = self.besideAnswer(grouping);
+    const room = asked.room orelse return null;
+    return switch (asked.answer orelse return null) {
         .split => sideFor(room.w, room.h),
         .into, .tab => null,
     };
diff --git a/plugins/workbench/src/Workspace.zig b/plugins/workbench/src/Workspace.zig
index b9ae713ac..a4eef97db 100644
--- a/plugins/workbench/src/Workspace.zig
+++ b/plugins/workbench/src/Workspace.zig
@@ -161,7 +161,7 @@ pub fn draw(self: *Workspace) !dvui.App.Result {
     // The person's pane, when it has the room for an open beside to split it: a tape that drops a
     // tab on the edge asks for this first, or skips the drop (`core.placement`).
     if (core.anchor.wanted() and runtime.workbench().open_workspace_grouping == self.grouping and
-        runtime.workbench().besideEdge() != null) core.anchor.mark(pane_box, "workbench.beside-room", .{});
+        runtime.workbench().besideEdge(self.grouping) != null) core.anchor.mark(pane_box, "workbench.beside-room", .{});
 
     if (tabs.len > 0) {
         self.dropSnapshot();
diff --git a/src/editor/Demo.zig b/src/editor/Demo.zig
index 2813e46c0..c83a31c1e 100644
--- a/src/editor/Demo.zig
+++ b/src/editor/Demo.zig
@@ -285,11 +285,8 @@ pub fn frame(self: *Demo) void {
             .tape => |bytes| self.playTape(bytes) catch {},
         }
     }
-    // A drop beside is aimed at where the workbench would split, as the room is now.
-    self.editor.app.layout.beside = if (self.active())
-        if (self.editor.workbench.besideEdge()) |side| std.meta.stringToEnum(SplitTree.Side, @tagName(side)) else null
-    else
-        null;
+    // A drop beside is aimed at where the workbench would split the target place, as its room is now.
+    self.editor.app.layout.beside = if (self.active()) .{ .ctx = self, .edge = besideEdge } else null;
     self.snapshot.beginFrame();
     self.live.frame();
     self.player.frame();
@@ -872,6 +869,26 @@ fn commandTitle(ctx: *anyopaque, id: []const u8) ?[]const u8 {
     return c.title;
 }
 
+/// The edge a drop beside aims at over place `name`: where the workbench would split the pane
+/// shown there (a pane of its own tree is named for its grouping). A pane the layout's keywords
+/// show is in no list, so Main is the person's pane.
+pub fn besideEdge(ctx: *anyopaque, name: []const u8) ?SplitTree.Side {
+    const editor = from(ctx).editor;
+    const wb = &editor.workbench;
+    const grouping = Editor.Workspace.groupingOfName(name) orelse editor.workspaces.groupingIn(name) orelse blk: {
+        const main = editor.regionFor(sdk.keywords.ide.main) orelse return null;
+        if (!std.mem.eql(u8, main.name, name)) return null;
+        var layout = Editor.Layout.init(&editor.app.host, &editor.app.layout, editor.app.gpa, editor.app.host.arena());
+        var buf: [64]u8 = undefined;
+        const id = std.mem.print(&buf, Editor.Workspaces.id_prefix ++ "{d}", .{wb.open_workspace_grouping}) catch return null;
+        if (Editor.Layout.ViewDrag.holderOf(&layout, id)) |holder| {
+            if (!std.mem.eql(u8, holder, name)) return null;
+        }
+        break :blk wb.open_workspace_grouping;
+    };
+    return wb.besideEdge(grouping);
+}
+
 /// The place a role names, by what it is rather than what the person's layout calls it.
 fn resolveRole(ctx: *anyopaque, role: []const u8, buf: []u8) ?[]const u8 {
     const keywords = if (std.mem.eql(u8, role, "documents"))
diff --git a/src/editor/Workspaces.zig b/src/editor/Workspaces.zig
index 1c1bfda8a..0e31bfa65 100644
--- a/src/editor/Workspaces.zig
+++ b/src/editor/Workspaces.zig
@@ -289,18 +289,29 @@ fn layoutOf(editor: *Editor) Layout {
     return Layout.init(&editor.app.host, &editor.app.layout, editor.app.gpa, editor.app.host.arena());
 }
 
+/// The pane shown in place `name`: the person's own when it is there, else the first held.
+/// Null where the place holds no pane (a pane the keywords show is in no list: the caller's).
+pub fn groupingIn(self: *Workspaces, name: []const u8) ?u64 {
+    const editor = self.editorOf();
+    var l = layoutOf(editor);
+    var buf: [64]u8 = undefined;
+    var first: ?u64 = null;
+    for (self.views.keys()) |g| {
+        const holder = Layout.ViewDrag.holderOf(&l, viewId(&buf, g)) orelse continue;
+        if (!std.mem.eql(u8, holder, name)) continue;
+        if (g == editor.workbench.open_workspace_grouping) return g;
+        first = first orelse g;
+    }
+    return first;
+}
+
 fn beside(ctx: *anyopaque, grouping: u64, anchor: u64, side: Workbench.Panes.Side, adaptive: bool) bool {
     const self: *Workspaces = @ptrCast(@alignCast(ctx));
     const editor = self.editorOf();
     var l = layoutOf(editor);
     var abuf: [64]u8 = undefined;
     const place = Layout.ViewDrag.holderOf(&l, viewId(&abuf, anchor)) orelse return false;
-    const new = Layout.splitOn(&l, place, switch (side) {
-        .left => .left,
-        .right => .right,
-        .top => .top,
-        .bottom => .bottom,
-    }) orelse return false;
+    const new = Layout.splitOn(&l, place, side) orelse return false;
     var buf: [64]u8 = undefined;
     const id = l.arena.dupe(u8, viewId(&buf, grouping)) catch return false;
     l.state.assign(l.gpa, new, &.{id}) catch return false;
@@ -354,12 +365,7 @@ fn open(ctx: *anyopaque, grouping: u64, side: Workbench.Panes.Side) bool {
     var l = layoutOf(self.editorOf());
     var buf: [64]u8 = undefined;
     const place = Layout.ViewDrag.holderOf(&l, viewId(&buf, grouping)) orelse return false;
-    return Layout.splitOn(&l, place, switch (side) {
-        .left => .left,
-        .right => .right,
-        .top => .top,
-        .bottom => .bottom,
-    }) != null;
+    return Layout.splitOn(&l, place, side) != null;
 }
 
 /// The view of the workspace whose only tab is document `id`, if one is.
diff --git a/tests/integration.zig b/tests/integration.zig
index a2340a78a..dc4cba703 100644
--- a/tests/integration.zig
+++ b/tests/integration.zig
@@ -5547,6 +5547,71 @@ test "dragging a view over its own place shows that place's drop zones" {
     try std.testing.expect(fizzy.core.widgets.DropZones.showing(center.id));
 }
 
+test "drop: beside marks the tall target's bottom rather than the wide source's right" {
+    var ctx = try shim.init(std.testing.allocator);
+    defer ctx.deinit(std.testing.allocator);
+    const editor = ctx.editor;
+    const gpa = std.testing.allocator;
+    editor.app.gpa = gpa;
+    const state = &editor.app.layout;
+    defer state.regions.deinit(gpa);
+    defer state.regions_building.deinit(gpa);
+    defer state.deinitExtents(gpa);
+    defer state.deinitAssignments(gpa);
+    defer state.deinitQualified(gpa);
+    defer state.view_drag.discard(gpa);
+    const source: dvui.Rect.Physical = .{ .x = 0, .y = 0, .w = 1200, .h = 800 };
+    const target: dvui.Rect.Physical = .{ .x = 1200, .y = 0, .w = 820, .h = 1180 };
+    state.registerRegion(gpa, .{ .name = "Source", .keywords = fizzy.sdk.keywords.ide.main, .bounds = source, .size = .{ .w = source.w, .h = source.h } });
+    state.registerRegion(gpa, .{ .name = "Target", .keywords = &.{"slot"}, .bounds = target, .size = .{ .w = target.w, .h = target.h } });
+    state.publishRegions();
+    const Probe = struct {
+        calls: usize = 0,
+        fn edge(raw: *anyopaque, name: []const u8) ?fizzy.Editor.Layout.State.SplitTree.Side {
+            const self: *@This() = @ptrCast(@alignCast(raw));
+            self.calls += 1;
+            const room = if (std.mem.eql(u8, name, "Target")) target else source;
+            return workbench.Workbench.sideFor(room.w, room.h);
+        }
+    };
+    var probe: Probe = .{};
+    state.beside = .{ .ctx = &probe, .edge = Probe.edge };
+    defer state.beside = null;
+    try editor.app.host.registerSurface(.{ .id = "test.view", .title = "View", .keywords = &.{"slot"}, .draw = ManyPanelFrame.draw });
+    try state.assign(gpa, "Source", &.{"test.view"});
+    var layout = fizzy.Editor.Layout.init(&editor.app.host, state, gpa, dvui.currentWindow().arena());
+    const VD = fizzy.Editor.Layout.ViewDrag;
+    const cw = dvui.currentWindow();
+    const mouse = cw.mouse_pt;
+    defer cw.mouse_pt = mouse;
+    cw.mouse_pt = source.center();
+    VD.begin(&layout, "Source", source, source);
+    cw.mouse_pt = target.center();
+    fizzy.core.anchor.want();
+    VD.drawZones(&layout, "Target", dvui.parentGet().extendId(@src(), 0));
+    const beside = dvui.tagGet("drop:beside") orelse return error.TestUnexpectedResult;
+    const bottom = dvui.tagGet("drop:bottom") orelse return error.TestUnexpectedResult;
+    const right = dvui.tagGet("drop:right") orelse return error.TestUnexpectedResult;
+    try std.testing.expectEqual(bottom.rect, beside.rect);
+    try std.testing.expect(!std.meta.eql(right.rect, beside.rect));
+    try std.testing.expectEqual(@as(usize, 1), probe.calls);
+
+    // Main's implicit pane must not borrow the shape of a workspace held elsewhere.
+    const wb = &editor.workbench;
+    const grouping = wb.open_workspace_grouping;
+    var workspace = workbench.Workspace.init(grouping);
+    workspace.pane_rect_physical = source;
+    try wb.workspaces.put(gpa, grouping, workspace);
+    defer wb.workspaces.deinit(gpa);
+    var id_buf: [64]u8 = undefined;
+    const id = try std.mem.print(&id_buf, fizzy.Editor.Workspaces.id_prefix ++ "{d}", .{grouping});
+    try editor.app.host.registerSurface(.{ .id = id, .title = "Workspace", .keywords = &.{"slot"}, .draw = ManyPanelFrame.draw });
+    try state.assign(gpa, "Target", &.{id});
+    editor.demo.editor = editor;
+    editor.app.host.installFizzyApi(.{ .ctx = editor, .vtable = &fizzy.Editor.fizzy_api_vtable });
+    try std.testing.expectEqual(@as(?fizzy.Editor.Layout.State.SplitTree.Side, null), fizzy.Editor.Demo.besideEdge(&editor.demo, "Source"));
+}
+
 // `core` is not a test root, so its widgets' pure rules are tested here.
 const DZ = fizzy.core.widgets.DropZones;
 
@@ -11030,6 +11095,26 @@ test "headless: the whole editor comes up, opens a file, plays the tour and goes
         // With another pane there, it takes the view; without, the person's own does.
         const taken = wb.besideGrouping();
         if (others > 0) try std.testing.expect(taken != here) else try std.testing.expectEqual(here, taken);
+        // A demo's `drop:beside` is the answer for the place it is aimed at, not the person's pane's
+        // for every place: Main's is the pane's edge in its own room, which turns with the room,
+        // and a place that holds no documents has none.
+        if (others == 0) {
+            const Side = fizzy.core.widgets.DockLayout.Side;
+            const main = (editor.regionFor(fizzy.sdk.keywords.ide.main) orelse return error.TestUnexpectedResult).name;
+            const sidebar = (editor.regionFor(fizzy.sdk.keywords.ide.sidebar) orelse return error.TestUnexpectedResult).name;
+            ws.pane_rect_physical = .{ .x = 0, .y = 0, .w = 1200 * s, .h = 800 * s };
+            try std.testing.expectEqual(@as(?Side, .right), fizzy.Editor.Demo.besideEdge(&editor.demo, main));
+            try std.testing.expectEqual(@as(?Side, null), fizzy.Editor.Demo.besideEdge(&editor.demo, sidebar));
+            ws.pane_rect_physical = .{ .x = 0, .y = 0, .w = 820 * s, .h = 1180 * s };
+            try std.testing.expectEqual(@as(?Side, .bottom), fizzy.Editor.Demo.besideEdge(&editor.demo, main));
+            var pane_buf: [32]u8 = undefined;
+            const pane = fizzy.Editor.Workspace.name(&pane_buf, here);
+            try std.testing.expectEqual(@as(?Side, .bottom), fizzy.Editor.Demo.besideEdge(&editor.demo, pane));
+            var other_buf: [32]u8 = undefined;
+            try std.testing.expectEqual(@as(?Side, null), fizzy.Editor.Demo.besideEdge(&editor.demo, fizzy.Editor.Workspace.name(&other_buf, here + 1000)));
+            try std.testing.expectEqual(@as(?Side, null), wb.besideEdge(here + 1000));
+            ws.pane_rect_physical = .{ .x = 0, .y = 0, .w = 390 * s, .h = 844 * s };
+        }
         try std.testing.expectEqual(fizzy.core.widgets.DockLayout.Side.right, workbench.Workbench.sideFor(1200, 800));
         try std.testing.expectEqual(fizzy.core.widgets.DockLayout.Side.bottom, workbench.Workbench.sideFor(820, 1180));
     }