Add xy.tooltip(mode="x"): a shared-axis tooltip with cursor and active dots

docs/components/tooltips.md

@@ -193,6 +193,45 @@ See [Events and callbacks](/docs/xy/api-reference/events-and-callbacks/) for
 hover payloads and [Marks and components reference](/docs/xy/api-reference/marks-and-components/)
 for the exact tooltip signature.
 
+## Shared Tooltip Along an Axis
+
+`xy.tooltip(mode="x")` turns the tooltip into an axis tooltip, the model
+Recharts uses by default and Plotly calls `hovermode="x unified"`. The pointer
+only has to be inside the plot: its horizontal position snaps to the nearest x
+value and every series' point at that x is listed at once, while the vertical
+position is ignored. The plot divides into full-height bands with boundaries
+halfway between adjacent points, a cursor line marks the selected x, each
+series shows an active dot, and the tooltip follows the pointer. Bars join by
+their footprint: a grouped bar chart lists every series of the category under
+the pointer, with one cursor on the category centre — and no active dots, since
+the bar is already the mark. `mode="y"` does the same along
+the y axis — useful for horizontal layouts, but available on any Cartesian
+chart. The default, `mode="nearest"`, keeps the 12 px nearest-point behavior.
+
+~~~python demo exec
+import reflex_xy
+import xy
+
+pages = ["Page A", "Page B", "Page C", "Page D", "Page E", "Page F", "Page G"]
+shared_tooltip_chart = xy.line_chart(
+    xy.line(pages, [2400, 1398, 9800, 3908, 4800, 3800, 4300], name="pv", color="#8884d8", width=2),
+    xy.line(pages, [4000, 3000, 2000, 2780, 1890, 2390, 3490], name="uv", color="#82ca9d", width=2),
+    xy.tooltip(mode="x"),
+    xy.legend(loc="upper right"),
+    title="Hover anywhere above a page",
+)
+
+
+def shared_tooltip_demo():
+    return reflex_xy.chart(shared_tooltip_chart, height="320px")
+~~~
+
+`fields=`, `format=`, and `title=` keep their meaning: the title template
+resolves against the first series' row, and each series row shows the
+requested fields (minus the band axis, which is already the title). Style the
+cursor line through the `tooltip_cursor` slot or the `--chart-crosshair`
+token it shares with the crosshair.
+
 ## FAQ
 
 ### How do I show values on hover in a Python chart?

docs/styling/capabilities.md

@@ -12,7 +12,7 @@ and *does the change survive where I need it*. This page answers both from the
 registry the implementation is checked against.
 
 - **11** mark style properties across **22** mark kinds, drawn by all three renderers.
-- **48** stable chrome slots for CSS and Tailwind in the browser.
+- **49** stable chrome slots for CSS and Tailwind in the browser.
 - **1** way to add a mark kind XY does not ship, without forking it.
 
 ## Mark style properties
@@ -79,6 +79,7 @@ token bag or in mark and axis `style=`, which every renderer reads.
 | `tooltip_row` | full | none | none |
 | `tooltip_label` | full | none | none |
 | `tooltip_value` | full | none | none |
+| `tooltip_cursor` | full | none | none |
 | `modebar` | full | none | none |
 | `modebar_drag_handle` | full | none | none |
 | `modebar_control_group` | full | none | none |

docs/styling/chrome-slots.md

@@ -38,6 +38,7 @@ primitive or structural descendant is a separate DOM element.
 | `tooltip_row` | One tooltip field row |
 | `tooltip_label` | One tooltip field label |
 | `tooltip_value` | One formatted tooltip value |
+| `tooltip_cursor` | Line across the plot at the shared-tooltip band coordinate — vertical for `xy.tooltip(mode="x")`, horizontal for `mode="y"` |
 | `modebar` | Mode/tool bar container |
 | `modebar_drag_handle` | Draggable grip revealed beside the toolbar |
 | `modebar_control_group` | Selection, pan, and export control group |
@@ -358,8 +359,8 @@ apply it with. Rather than leave that to be discovered, it is a contract:
 | --- | --- | --- | --- |
 | mark / axis `style=` | yes | yes | yes |
 | chart-level `style=` (design tokens) | yes | yes | yes |
-| `styles={slot: {...}}` | yes, all 48 slots | text subset, 9 slots | text subset, 9 slots |
-| `class_names={slot: "..."}` | yes, all 48 slots | dropped | dropped |
+| `styles={slot: {...}}` | yes, all 49 slots | text subset, 9 slots | text subset, 9 slots |
+| `class_names={slot: "..."}` | yes, all 49 slots | dropped | dropped |
 | `custom_css=` | yes | raises | raises |
 | `xy.legend(style=...)` | yes | 6 keys | 6 keys |
 | `xy.colorbar(style=...)` | yes | dropped | dropped |

js/src/20_theme.ts

@@ -186,6 +186,7 @@ export const XY_CHROME_CSS = `
 :where(.xy [data-xy-selection-lasso-handle]){fill:var(--chart-bg,#fff);stroke:var(--chart-selection,var(--xy-selection));stroke-width:1.5;cursor:grab;pointer-events:all}
 :where(.xy [data-xy-selection-lasso-handle][data-xy-active]){cursor:grabbing;fill:var(--chart-selection,var(--xy-selection))}
 :where(.xy [data-xy-slot="crosshair_x"],.xy [data-xy-slot="crosshair_y"]){background:var(--chart-crosshair,rgba(15,23,42,.42))}
+:where(.xy [data-xy-slot="tooltip_cursor"]){background:var(--chart-crosshair,rgba(15,23,42,.42))}
 :where(.xy [data-xy-slot="axis_band"]){cursor:var(--xy-axis-band-cursor)}
 :where(.xy [data-xy-slot="axis_line"],.xy [data-xy-slot="tick_mark"]){width:var(--xy-axis-rule-width);height:var(--xy-axis-rule-height);background:var(--xy-axis-rule-paint)}
 :where(.xy [data-xy-slot="tick_label"]){color:var(--chart-text,inherit)}