Fix #522: SVG round trips keep hidden objects and data-* attributes

An SVG used as an animation rig lost its hidden alternates and their
rotation pivots: the exporter left hidden objects out (only hidden layers
could be kept), and the importer dropped data-* attributes.

- SVG export: hiddenLayers (on by default for document.save, as before)
  now keeps hidden objects too, each written display="none" on its own
  element (path, image, text or group). Exports still leave them out
  unless asked; the CLI's convert asks, as a conversion keeps the
  document.
- An object's own data: ObjectAttributes.data, the data-* attributes in
  order (ours, data-name and data-vc-*, aside). The importer keeps them on
  the objects and layers they belong to (at most 64 per element), the
  exporter writes them back, the native format saves them (missing in
  older files), and object.setProps {data: {key: value|null}} sets or
  removes them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ROADMAP.md

@@ -4,7 +4,7 @@ VectorCraft is a clean-room, open-source, pure-Rust reimplementation of the Adob
 
 This file tracks **how far we are and what's left**. Time estimates are wall-clock hours of continuous Claude Opus 5.5 agent work (including builds and the CI gate), given both for **one agent** and for **4–6 parallel agents** on disjoint crates. They are counted from the remaining work (see [Parity estimate](#parity-estimate)), calibrated against measured throughput, and updated as work lands.
 
-_Last updated: 2026-10-09 (after placed documents (File › Place of a `.vectorcraft` file, linked), M4.14–M4.98, M8.1–M8.20, M14.4–M14.7, the MCP prompts, resource templates, completions and logging, the 2026-10-07 issue fixes, the Layers panel rework and the 2026-10-08 community contributions: Pen and shape-tool modifiers, path editing, Layers, Artboards, Swatches/Brushes and dialogs, Japanese composition and PDF text, Hebrew/Arabic type, interface languages (Spanish among them), the font menu, saved selections, MCP and EPS, the missing-font export warning (#319), open paths in the Shape Builder (#374), PDF/`.ai` import keeping strokes live and hidden and nested layers (#372), per-corner Live Corners (#381), SVG type opening at the size it draws at (#396), the Wayland clipboard with copied-file paste (#398), ruler guides that can be selected, moved and deleted (#414), two batches of Preferences options that were stored but unused (#394), skeleton reads with `document.find` for large documents over MCP (#416) and anchors dragged with Direct Selection snapping to points, segments and smart guides, clipped SVG layers opening as clipping layers (#420), PDF/`.ai` layers read on pages of tens of millions of operators (#419), Document Color Mode putting RGB greys on the black plate on request and converting pattern tiles (#421) and movable dialogs with Offset Path's Joins dropdown (#423) and numeric fields scrubbed by dragging their label (#400), stroke weight presets in the stroke unit (#426), the Appearance panel's Opacity popup (#430), type on a path brackets, flip and Type on a Path Options that keep the type in place (#429), Layers rows dragged with a ghost and dropped on the trash or New Layer (#435), tool flyouts opening on a right or corner press (#436), tool flyouts torn off into floating toolbars (#437), the Shape Builder's erase mode deleting edges too (#439), installed fonts registered outside the font folders and fonts installed while the app runs listed in the font menus (#443), alike circular corners on rectangles that aren't square (#442), tool cursors as OS cursors so the pointer no longer trails over the canvas (#444), artboards copied and pasted with their art (#446), guides dragged out of the rulers snapping to the art's side midpoints and the artboards, artboard guides (#451), the toolbar's double arrow and Window › Toolbars › Double Column switching between one and two columns in any window height (#455), the Smart Guides display options and Snapping Tolerance (#394), Font Size and Leading combo boxes with preset lists in the Character and Properties panels and the Control bar (#458), screenshots pasted from the clipboard on macOS, Windows and the web (#457), the Properties panel's Fill and Stroke matching the Control bar's, Illustrator's Window menu panel keys (Shift+F7 for Align…) and Alt-wheel zoom whatever the wheel preference (Discord feedback), the point/area type widget (Discord feedback), groups in legacy Illustrator .ai files (Discord feedback), a rotating desktop log file (#465), image controls in the Control bar and Properties panel: Image Trace with its presets, Mask, Crop Image, Embed/Unembed, and an Image Trace object's preset, Expand and Release (Discord feedback), the Pen working as the Anchor Point tool with Alt held over a selected path's handles and anchors, and anchor buttons that convert, connect and cut paths at the selected anchors (Discord feedback), Japanese hanging punctuation (burasagari, #463), Escape leaving Presentation Mode with no screen mode saved across restarts, documents dropped on the desktop app opening as tabs of their own and a note that an `.ai` file's art off its artboards isn't in the part read (#472), Add/Delete Anchor Point tool icons drawn from the Pen tool's (#479), EPS import running more of PostScript Level 3 (patterns, Type 3 fonts, mesh shadings, masked images, VM and resource probes), and a preview that stands in saying why (Discord feedback, #466, #469, #474), chords with modifiers recorded in Edit › Keyboard Shortcuts (#487), Type Object Selection by Path Only (#394), Anti-aliased Artwork (#394), Show Pixel Grid (#394), pen and touch taps pressed and lifted within one frame clicking where they tapped and the Linux/Wayland pen-tablet workaround (#491), bounding-box resizes landing on the other objects' anchors and centres with labels, and the Rotate, Scale, Shear and Reflect tools snapping their drags (#482), Shift-drag marquees that toggle the objects or anchors they reach and a Lasso whose Alt subtraction keeps the rest of the selection (#483), the mouse wheel stepping the focused numeric field, the dialogs' and preferences' drag values made such fields (#485), Show The Home Screen When No Documents Are Open (#394), Numbers Without Units Are Points (#394), Auto-Collapse Iconic Panels (#394), the Contextual Task Bar moved by its handle and its More Options menu pinning and resetting its position, a designed macOS DMG windoLine truncated
+_Last updated: 2026-10-09 (after placed documents (File › Place of a `.vectorcraft` file, linked), M4.14–M4.98, M8.1–M8.20, M14.4–M14.7, the MCP prompts, resource templates, completions and logging, the 2026-10-07 issue fixes, the Layers panel rework and the 2026-10-08 community contributions: Pen and shape-tool modifiers, path editing, Layers, Artboards, Swatches/Brushes and dialogs, Japanese composition and PDF text, Hebrew/Arabic type, interface languages (Spanish among them), the font menu, saved selections, MCP and EPS, the missing-font export warning (#319), open paths in the Shape Builder (#374), PDF/`.ai` import keeping strokes live and hidden and nested layers (#372), per-corner Live Corners (#381), SVG type opening at the size it draws at (#396), the Wayland clipboard with copied-file paste (#398), ruler guides that can be selected, moved and deleted (#414), two batches of Preferences options that were stored but unused (#394), skeleton reads with `document.find` for large documents over MCP (#416) and anchors dragged with Direct Selection snapping to points, segments and smart guides, clipped SVG layers opening as clipping layers (#420), PDF/`.ai` layers read on pages of tens of millions of operators (#419), Document Color Mode putting RGB greys on the black plate on request and converting pattern tiles (#421) and movable dialogs with Offset Path's Joins dropdown (#423) and numeric fields scrubbed by dragging their label (#400), stroke weight presets in the stroke unit (#426), the Appearance panel's Opacity popup (#430), type on a path brackets, flip and Type on a Path Options that keep the type in place (#429), Layers rows dragged with a ghost and dropped on the trash or New Layer (#435), tool flyouts opening on a right or corner press (#436), tool flyouts torn off into floating toolbars (#437), the Shape Builder's erase mode deleting edges too (#439), installed fonts registered outside the font folders and fonts installed while the app runs listed in the font menus (#443), alike circular corners on rectangles that aren't square (#442), tool cursors as OS cursors so the pointer no longer trails over the canvas (#444), artboards copied and pasted with their art (#446), guides dragged out of the rulers snapping to the art's side midpoints and the artboards, artboard guides (#451), the toolbar's double arrow and Window › Toolbars › Double Column switching between one and two columns in any window height (#455), the Smart Guides display options and Snapping Tolerance (#394), Font Size and Leading combo boxes with preset lists in the Character and Properties panels and the Control bar (#458), screenshots pasted from the clipboard on macOS, Windows and the web (#457), the Properties panel's Fill and Stroke matching the Control bar's, Illustrator's Window menu panel keys (Shift+F7 for Align…) and Alt-wheel zoom whatever the wheel preference (Discord feedback), the point/area type widget (Discord feedback), groups in legacy Illustrator .ai files (Discord feedback), a rotating desktop log file (#465), image controls in the Control bar and Properties panel: Image Trace with its presets, Mask, Crop Image, Embed/Unembed, and an Image Trace object's preset, Expand and Release (Discord feedback), the Pen working as the Anchor Point tool with Alt held over a selected path's handles and anchors, and anchor buttons that convert, connect and cut paths at the selected anchors (Discord feedback), Japanese hanging punctuation (burasagari, #463), Escape leaving Presentation Mode with no screen mode saved across restarts, documents dropped on the desktop app opening as tabs of their own and a note that an `.ai` file's art off its artboards isn't in the part read (#472), Add/Delete Anchor Point tool icons drawn from the Pen tool's (#479), EPS import running more of PostScript Level 3 (patterns, Type 3 fonts, mesh shadings, masked images, VM and resource probes), and a preview that stands in saying why (Discord feedback, #466, #469, #474), chords with modifiers recorded in Edit › Keyboard Shortcuts (#487), Type Object Selection by Path Only (#394), Anti-aliased Artwork (#394), Show Pixel Grid (#394), pen and touch taps pressed and lifted within one frame clicking where they tapped and the Linux/Wayland pen-tablet workaround (#491), bounding-box resizes landing on the other objects' anchors and centres with labels, and the Rotate, Scale, Shear and Reflect tools snapping their drags (#482), Shift-drag marquees that toggle the objects or anchors they reach and a Lasso whose Alt subtraction keeps the rest of the selection (#483), the mouse wheel stepping the focused numeric field, the dialogs' and preferences' drag values made such fields (#485), Show The Home Screen When No Documents Are Open (#394), Numbers Without Units Are Points (#394), Auto-Collapse Iconic Panels (#394), the Contextual Task Bar moved by its handle and its More Options menu pinning and resetting its position, a designed macOS DMG windoLine truncated
 
 ## Where we are
 
@@ -156,7 +156,7 @@ grade by behaviour against `plan/illustrator/`, not by whether a menu item exist
 - **Fonts:** a font is found by any of its names (family and style in every language of its name table, legacy family/style pairs, PostScript name), so documents from other apps open with the font they name; Find Font and `text.fonts` say for each font whether it was found exactly, by another name, substituted or missing, and how many glyphs are missing. PDF and `.ai` import brings Japanese text back as live type: CID fonts without a ToUnicode map read through the standard CMaps, vertical columns (WMode 1) as vertical type, letter spacing as tracking; a glyph is live type only when the installed font (in the closest style of its family) draws the same glyph, and text in a font that isn't installed comes in as live type shown in the fallback font until the font is installed (exports that draw it — PDF, EPS, EMF/WMF, raster, SVG outlines or embedded fonts — warn that they wrote the fallback font; `textAs: outlines` keeps the PDF's embedded glyphs).
 - **Files (M4):**
   - `.vectorcraft` (lossless JSON, compressed, atomic saves, save down to v1), Save As with a format chooser, Save a Copy, Revert, templates, Data Recovery after a crash (browser tabs hold their copies with Web Locks too, so a background tab's copies are never taken for a crash's, and a tab repairs copies another removed when it resumes: #367), background save and export. The desktop app writes its warnings and errors (graphics adapter, a lost graphics device, panics the guard recovered from) to standard error and to `logs/vectorcraft.log` next to the preferences, the two previous runs kept and each file capped at 16 MiB, so a launch without a terminal still leaves something to attach to a bug report (#465).
-  - SVG/SVGZ in and out with SVG Options, Preserve Editing, symbols, filters, rich text and physical units (SVG type under a transform or `viewBox` scale opens at the size it draws at, the scale moved into its size, leading, baseline shift and strokes, a stretch, skew or rotation kept as its transform: #396; a top-level group with a clip path, such as a clipped Inkscape layer, opens as a layer with a clipping mask, its name kept: #420); PDF and PDF-compatible `.ai` in and out (layers, with hidden ones kept hidden with their art and nested ones as sublayers, on pages of up to 64 million operators, art whose layer can't be told going to a hidden, non-printing layer rather than showing or printing: #419; strokes kept live, a fill and a stroke of one outline as one object; a type object's stroke written as each glyph's outline stroked back on the type, so it stays one editable object; lines wrapped in a frame (each wrapped line ending in a space, one left edge, leading and font) back as one area type object, left aligned or justified with its paragraph spacing, where laying it out breaks the lines where the file does; glyphs set apart by gaps wider than a space (a barcode's digit groups) keeping their places; layers stacked as the pages mark them even when one first paints on a later page, art ending a layer's marked content or a clip closing in a later layer kept in its own layer, and layers with no art kept empty: #508; masks, editable text with type set along a curve coming back as type on a path, each artboard's art on its own page only, an `.ai`'s white page under its layers left out rather than coming in as art, spot colours, presets, security, marks and bleed, ICC output intents, raster effects, subset fonts, PDF/X, PDF layers, overprint, page thumbnails, fast web view, PDF 1.3). CMYK images keep their ink amounts from PDF import (and from placed CMYK TIFFs) to PDF export: a CMYK JPEG passes through unchanged, others stay CMYK (DeviceCMYK, or ICC-based CMYK in PDF/X-3/X-4) unless the Output settings convert them; the canvas shows them through the working CMYK profile (#320).
+  - SVG/SVGZ in and out with SVG Options, Preserve Editing, symbols, filters, rich text and physical units (SVG type under a transform or `viewBox` scale opens at the size it draws at, the scale moved into its size, leading, baseline shift and strokes, a stretch, skew or rotation kept as its transform: #396; a top-level group with a clip path, such as a clipped Inkscape layer, opens as a layer with a clipping mask, its name kept: #420; hidden objects written hidden on Save and `convert`, and `data-*` attributes kept as the objects' own data: #522); PDF and PDF-compatible `.ai` in and out (layers, with hidden ones kept hidden with their art and nested ones as sublayers, on pages of up to 64 million operators, art whose layer can't be told going to a hidden, non-printing layer rather than showing or printing: #419; strokes kept live, a fill and a stroke of one outline as one object; a type object's stroke written as each glyph's outline stroked back on the type, so it stays one editable object; lines wrapped in a frame (each wrapped line ending in a space, one left edge, leading and font) back as one area type object, left aligned or justified with its paragraph spacing, where laying it out breaks the lines where the file does; glyphs set apart by gaps wider than a space (a barcode's digit groups) keeping their places; layers stacked as the pages mark them even when one first paints on a later page, art ending a layer's marked content or a clip closing in a later layer kept in its own layer, and layers with no art kept empty: #508; masks, editable text with type set along a curve coming back as type on a path, each artboard's art on its own page only, an `.ai`'s white page under its layers left out rather than coming in as art, spot colours, presets, security, marks and bleed, ICC output intents, raster effects, subset fonts, PDF/X, PDF layers, overprint, page thumbnails, fast web view, PDF 1.3). CMYK images keep their ink amounts from PDF import (and from placed CMYK TIFFs) to PDF export: a CMYK JPEG passes through unchanged, others stay CMYK (DeviceCMYK, or ICC-based CMYK in PDF/X-3/X-4) unless the Output settings convert them; the canvas shows them through the working CMYK profile (#320).
   - EPS and DXF in and out, EMF/WMF in and out; PNG (with PNG-8), JPEG, WebP, GIF, TIFF, BMP, Targa and layered PSD export. EPS import runs a PostScript Level 3 interpreter written from the PostScript Language Reference: resource categories and `resourceforall`, local and global VM (`currentglobal`/`setglobal`/`gcheck`), `clipsave`/`cliprestore`, subarrays and substrings that share storage, the standard dictionaries in `systemdict`, `dictstack`, `internaldict`, executable filters and strings, `load` by any key, `//name` immediate names, `token`, `execform`, user paths, `cshow`, `rootfont`, `cachestatus`, colour rendering and halftone queries, file `status` and data read with `flushfile`, and `pdfmark` marks dropped (Discord feedback, #466, #469, #474). Masked images (`ImageType 3` in its three interleavings) and reusable streams are read, and an image's several data sources are read in turn, as the reference defines (procedures that read one file get their own rows: such images came in banded, #498). `restore` puts dictionaries back as they were at the `save`, so programs that count their saves in a dictionary read to their end (part of #505). Tiling patterns come in as pattern swatches, uncoloured ones too; Type 3 fonts' glyphs as their outlines, spaced by `ashow`/`widthshow`/`xshow`/`kshow`; mesh and function-based shadings (types 1, 4–7) as gradient meshes; sampled functions (type 0) and Flate/LZW predictors are read. It is tested with programs written from the specification in the ways common generators use these features; Inkscape/cairo EPS files open as vectors. When a file's PostScript still can't be read, it opens as its TIFF preview, its Windows metafile preview (as vectors) or its EPSI preview, and the warning (in the status bar, `document.open`/`app.open`/MCP `open_file` replies and `vectorcraft-cli info`) names the error, the operator that raised it and the procedures it ran in. Legacy PostScript `.ai` files (Illustrator 3–8, written with the prolog that defines their operators) keep their groups and nested groups (`u` … `U`), between and inside clipping groups; EPS and EMF/WMF import nest clips (and groups) at most 128 deep, so a hostile file can't exhaust the stack. DXF TEXT justified Fit or Aligned spans its two points (stretched, or scaled as a whole).
   - Placed documents: File › Place of a `.vectorcraft` file links to it by default (`file.place`'s `link`): one locked object showing an artboard of the document (or its art's bounds), read the way placing it without Link reads it, its symbols, patterns and images kept apart from the document's; without Link (or from bytes, not a file) it is an editable copy as before. It stays vectors in every output (SVG, PDF, EPS, EMF, DXF), and so do placed documents inside it, read from their own files up to 8 levels deep (documents that place each other stop there). On screen they draw from bitmaps cached per file and zoom step, shared by every copy and made in the background (a placeholder until ready), so a sheet of them redraws in about a millisecond; exports and prints draw them exactly. Like linked images, a save keeps only a preview of each (JPEG when opaque) unless Include Linked Files; output, and zooming past the preview, read the file again, falling back to the preview with a warning when it is gone or changed. Saves for older versions write them as plain art. Links check, update, relink, Update Links on open, Link Info (the artboard's size), Placement Options, Break Link (also Embed, Object › Expand: the editable copy placing without Link gives, its resources joining the document), Edit Original (the document in a new tab) and the Links panel cover them; saving a document updates the open documents that place it. The native format (v4) keeps data of 8 KB or more after the JSON instead of base64 in it.
   - Place and the Links panel, Package, File Info, Print with print presets, PostScript output and print tiling, slices and Save for Web, Export for Screens and Asset Export, CSS Properties, PNG/PDF/SVG/text clipboard flavours; files copied in a file manager paste as art (SVG, PDF, EMF/WMF, bitmaps) on every desktop platform, and Linux/Wayland reads the compositor's clipboard (#398); on Linux the Paste menu checks the clipboard off the UI thread, so an X11 owner that never answers can't freeze the window (#510); screenshots and other copied pictures paste as embedded images at the view centre everywhere, the web included (#457).

apps/vectorcraft-cli/src/main.rs

@@ -69,7 +69,8 @@ USAGE:
       Open IN (any readable format) and export OUT in the format its extension picks (see Writable
       formats). --artboard is 0-based, --range 1-based (\"1-3,5\"); a PDF gets every artboard
       unless one of them is given, EPS the bounds of the art, the other formats the first artboard.
-      Live effects are kept; --outline-text writes SVG text as paths.
+      Live effects are kept, and hidden layers and objects (written hidden in SVG and PSD), with
+      SVG's data-* attributes; --outline-text writes SVG text as paths.
 
   vectorcraft-cli info FILE
       Print a JSON summary: the import warnings (what didn't come in as it was, such as an EPS
@@ -177,12 +178,10 @@ fn convert(args: &[String]) -> Result<(), String> {
     let [input, output] = <[String; 2]>::try_from(files).map_err(|_| "convert needs IN and OUT")?;
     let mut h = Headless::new();
     h.call("app.open", json!({"path": input})).map_err(|e| format!("open {input}: {e}"))?;
-    let r = h
-        .call(
-            "engine.execute",
-            json!({"command": "document.export", "params": {"path": output, "scale": scale, "artboard": artboard, "range": range, "outlineText": outline_text}}),
-        )
-        .map_err(|e| format!("export {output}: {e}"))?;
+    // A conversion keeps hidden layers and objects, written hidden, where the format can (SVG,
+    // PSD).
+    let params = json!({"path": output, "scale": scale, "artboard": artboard, "range": range, "outlineText": outline_text, "hiddenLayers": true});
+    let r = h.call("engine.execute", json!({"command": "document.export", "params": params})).map_err(|e| format!("export {output}: {e}"))?;
     outln!("{r}");
     Ok(())
 }

crates/doc/src/node.rs

@@ -1214,6 +1214,10 @@ pub struct ObjectAttributes {
     /// The note shown in the Attributes panel.
     #[serde(default, skip_serializing_if = "String::is_empty")]
     pub note: String,
+    /// The object's own data, in order: SVG's `data-*` attributes (`data-pivot="100,180"` is
+    /// `("pivot", "100,180")`), kept from import to export (`object.setProps {data}`).
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub data: Vec<(String, String)>,
 }
 
 /// The Attributes panel's Image Map shapes.

crates/engine/src/cmd/fileio/svg.rs

@@ -70,7 +70,7 @@ pub const OPTIONS: &[FormatOption] = &[
         name: "hiddenLayers",
         ty: "boolean",
         default: "false",
-        description: "keep hidden layers, not displayed (display:none); document.save sets it unless given",
+        description: "keep hidden layers and objects, not displayed (display=\"none\"); document.save sets it unless given",
     },
     FormatOption {
         name: "encoding",

crates/engine/src/cmd/object.rs

@@ -150,7 +150,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Object Properties",
             [],
             None,
-            "{ids?|id?, name?, visible?, locked?, opacity?: 0..100, blend?: \"Multiply\"…, isolate?, knockout?: \"on\"|\"off\"|\"neutral\"|bool (true = on, false = neutral), knockoutShape?: bool}",
+            "{ids?|id?, name?, visible?, locked?, opacity?: 0..100, blend?: \"Multiply\"…, isolate?, knockout?: \"on\"|\"off\"|\"neutral\"|bool (true = on, false = neutral), knockoutShape?: bool, data?: {key: \"value\" | null (removes it)} (the object's own data, SVG data-* attributes: {pivot: \"100,180\"} is data-pivot; document.node → attrs.data)}",
             has_doc,
             set_props
         ),
@@ -738,6 +738,32 @@ fn exit_isolation(s: &mut Session, _: &Value) -> Result<Value> {
     ok()
 }
 
+/// The most data entries `object.setProps` takes at once.
+const MAX_DATA: usize = 256;
+
+/// `object.setProps`'s `data`: each key (a data-* attribute's name: letters, digits, `-`, `_`,
+/// `.`) with its value, or `None` to remove it.
+fn data_param(m: &serde_json::Map<String, Value>) -> Result<Vec<(String, Option<String>)>> {
+    const C: &str = "object.setProps";
+    if m.len() > MAX_DATA {
+        return Err(bad(C, format!("data takes at most {MAX_DATA} keys at once")));
+    }
+    m.iter()
+        .map(|(k, v)| {
+            let k = k.strip_prefix("data-").unwrap_or(k);
+            if k.is_empty() || !k.chars().all(|c| c.is_ascii_alphanumeric() || matches!(c, '-' | '_' | '.')) || k == "name" || k.starts_with("vc-") {
+                return Err(bad(C, format!("data key `{k}`: letters, digits, -, _ and . (not name or vc-…)")));
+            }
+            let v = match v {
+                Value::Null => None,
+                Value::String(s) => Some(s.clone()),
+                other => Some(other.to_string()),
+            };
+            Ok((k.to_string(), v))
+        })
+        .collect()
+}
+
 fn set_props(s: &mut Session, p: &Value) -> Result<Value> {
     let ids = targets(s, p)?;
     let opacity = p.get("opacity").and_then(Value::as_f64).map(percent);
@@ -745,6 +771,11 @@ fn set_props(s: &mut Session, p: &Value) -> Result<Value> {
         Some(b) => Some(BlendMode::parse(b).ok_or_else(|| bad("object.setProps", format!("unknown blend mode `{b}`")))?),
         None => None,
     };
+    let data = match p.get("data") {
+        None | Some(Value::Null) => None,
+        Some(Value::Object(m)) => Some(data_param(m)?),
+        Some(v) => return Err(bad("object.setProps", format!("data must be an object of key: value, not {v}"))),
+    };
     let knockout = match p.get("knockout") {
         Some(v) => Some(
             Knockout::from_value(v)
@@ -779,6 +810,24 @@ fn set_props(s: &mut Session, p: &Value) -> Result<Value> {
             if let Some(v) = p.get("knockoutShape").and_then(Value::as_bool) {
                 n.knockout_shape = v;
             }
+            if let Some(changes) = &data {
+                n.edit_attrs(|a| {
+                    for (k, v) in changes {
+                        match (a.data.iter().position(|(key, _)| key == k), v) {
+                            (Some(i), Some(v)) => {
+                                if let Some(e) = a.data.get_mut(i) {
+                                    e.1 = v.clone();
+                                }
+                            }
+                            (Some(i), None) => {
+                                a.data.remove(i);
+                            }
+                            (None, Some(v)) => a.data.push((k.clone(), v.clone())),
+                            (None, None) => {}
+                        }
+                    }
+                });
+            }
         }
         Ok(())
     })?;

crates/engine/src/tests_attributes.rs

@@ -190,3 +190,27 @@ fn svg_export_links_objects_and_import_reads_the_links_back() {
     });
     assert_eq!(urls, [Some("https://example.com/?a=1&b=2".to_string()), None], "the link wraps the path alone");
 }
+
+/// #522: an object's own data (SVG `data-*` attributes) is set with `object.setProps {data}`,
+/// undone in one step, written to SVG and kept by the native format.
+#[test]
+fn object_data_is_set_saved_and_written_to_svg() {
+    let mut s = session();
+    let a = rect(&mut s, 10.0);
+    let data = |s: &Session| s.doc().unwrap().doc.node(a).unwrap().attrs.as_deref().map(|x| x.data.clone()).unwrap_or_default();
+    let pair = |k: &str, v: &str| (k.to_string(), v.to_string());
+    run(&mut s, "object.setProps", json!({"data": {"pivot": "60,100", "z": 3}}));
+    assert_eq!(data(&s), [pair("pivot", "60,100"), pair("z", "3")], "values are text");
+    run(&mut s, "object.setProps", json!({"data": {"data-pivot": "1,2", "z": null}}));
+    assert_eq!(data(&s), [pair("pivot", "1,2")], "a data- prefix is optional; null removes a key");
+    run(&mut s, "edit.undo", json!({}));
+    assert_eq!(data(&s).len(), 2, "one step");
+    for bad in [json!({"data": {"vc-x": "1"}}), json!({"data": {"name": "x"}}), json!({"data": {"a b": "1"}}), json!({"data": "pivot"})] {
+        assert!(s.execute("object.setProps", &bad).is_err(), "{bad}");
+    }
+    let svg = run(&mut s, "document.serialize", json!({"format": "svg"}))["text"].as_str().unwrap().to_string();
+    assert!(svg.contains("data-pivot=\"60,100\" data-z=\"3\""), "{svg}");
+    let native = vectorcraft_format::save(&s.doc().unwrap().doc, false);
+    let back = vectorcraft_format::load(&native).unwrap();
+    assert_eq!(back.node(a).unwrap().attrs, s.doc().unwrap().doc.node(a).unwrap().attrs);
+}

crates/svg/src/css.rs

@@ -50,9 +50,13 @@ pub(crate) fn blend_css(b: BlendMode) -> &'static str {
     }
 }
 
-/// An object's opacity, blend mode and isolation.
+/// An object's opacity, blend mode and isolation, and `display: none` when it is hidden (written
+/// only when hidden objects are kept).
 pub(crate) fn transparency(n: &Node) -> Props {
     let mut p = Props::new();
+    if !n.visible {
+        p.push(("display", "none".into()));
+    }
     if n.opacity < 1.0 {
         p.push(("opacity", fmt_num(n.opacity as f64, 3)));
     }

crates/svg/src/export.rs

@@ -545,15 +545,25 @@ impl Writer<'_> {
     }
     /// ` id="…"` for a named object, plus ` data-name="…"` with the name itself when the id had to
     /// differ from it (spaces, punctuation, duplicates, the unique prefix).
+    /// The id of `n`'s element (with its name when the id isn't it), then the object's own data
+    /// as `data-*` attributes.
     fn id_attr(&self, n: &Node) -> String {
         if self.anonymous {
             return String::new();
         }
-        let Some(id) = self.names.get(&n.id) else { return String::new() };
-        match n.name.as_deref() {
-            Some(name) if name != id => format!(" id=\"{}\" data-name=\"{}\"", xml_escape(id), xml_escape(name)),
-            _ => format!(" id=\"{}\"", xml_escape(id)),
+        let mut out = match (self.names.get(&n.id), n.name.as_deref()) {
+            (Some(id), Some(name)) if name != id => format!(" id=\"{}\" data-name=\"{}\"", xml_escape(id), xml_escape(name)),
+            (Some(id), _) => format!(" id=\"{}\"", xml_escape(id)),
+            (None, _) => String::new(),
+        };
+        for (k, v) in n.attrs.as_deref().map_or(&[][..], |a| a.data.as_slice()) {
+            // Names as XML takes them; ours (`name`, `vc-…`) are written by the export itself.
+            let valid = k.chars().all(|c| c.is_ascii_alphanumeric() || matches!(c, '-' | '_' | '.')) && k != "name" && !k.starts_with("vc-");
+            if valid && !k.is_empty() {
+                out.push_str(&format!(" data-{k}=\"{}\"", xml_escape(v)));
+            }
         }
+        out
     }
     fn matrix(&self, m: Affine) -> String {
         let c = m.as_coeffs();
@@ -1130,15 +1140,12 @@ impl Writer<'_> {
         std::mem::replace(&mut self.body, body)
     }
 
-    /// Props of a group (or layer): a knockout group is isolated, a hidden layer not displayed.
+    /// Props of a group (or layer): a knockout group is isolated, a hidden one not displayed.
     fn group_props(&self, n: &Node) -> Props {
         let mut p = css::transparency(n);
         if !n.isolate && n.knocks_out(self.knockout) {
             p.push(("isolation", "isolate".into()));
         }
-        if !n.visible {
-            p.push(("display", "none".into()));
-        }
         p
     }
 
@@ -1221,9 +1228,9 @@ impl Writer<'_> {
     }
 
     fn node_body(&mut self, n: &Node) {
-        // Hidden objects are left out; hidden layers too, unless the options keep them (hidden).
-        let kept = self.opts.hidden_layers && matches!(n.kind, NodeKind::Layer { template: false, .. });
-        if !(n.visible || kept) {
+        // Hidden layers and objects are left out, unless the options keep them (hidden). Template
+        // layers never print.
+        if !(n.visible || self.opts.hidden_layers) {
             return;
         }
         if has_raster(&n.appearance.effects) {

crates/svg/src/import.rs

@@ -64,6 +64,7 @@ pub(crate) fn import(svg: &str, opts: &ImportOptions) -> Result<(Document, Vec<S
         blends: fx::blends(&xml),
         files,
         non_scaling: found.non_scaling,
+        data: found.data,
         screen: (kx * ky).sqrt(),
     };
     if im.files.nested_text() {
@@ -124,6 +125,7 @@ pub(crate) fn import(svg: &str, opts: &ImportOptions) -> Result<(Document, Vec<S
             }
             im.add_unclipped(&mut l, 0, std::mem::take(&mut loose));
             l.visible = !im.hidden.contains(g.id());
+            im.keep_data(g.id(), &mut l);
             im.doc.layers.push(Arc::new(l));
         }
     } else {
@@ -210,6 +212,8 @@ struct Importer {
     files: files::Files,
     /// Ids of the shapes whose strokes don't scale ([`vector_effect`]).
     non_scaling: HashSet<String>,
+    /// The `data-*` attributes of elements, by id ([`user_data`]).
+    data: HashMap<String, Vec<(String, String)>>,
     /// Points per screen pixel (the root's user unit before its `viewBox`): what a non-scaling
     /// stroke's width is measured in.
     screen: f64,
@@ -320,6 +324,8 @@ struct Found {
     files: files::Files,
     /// Ids of the shapes whose strokes don't scale ([`vector_effect`]).
     non_scaling: HashSet<String>,
+    /// The `data-*` attributes of elements, by id ([`user_data`]).
+    data: HashMap<String, Vec<(String, String)>>,
     warnings: Vec<String>,
 }
 
@@ -390,7 +396,7 @@ impl Edits {
 fn prepass<'s>(svg: &'s str, opts: &ImportOptions) -> (Cow<'s, str>, Found) {
     let mut found = Found::default();
     // (`:` for prefixed elements such as `<svg:image>`.)
-    if !["<a", "display", "<use", ":use", "<image", ":image", vector_effect::NON_SCALING].iter().any(|t| svg.contains(t)) {
+    if !["<a", "display", "<use", ":use", "<image", ":image", vector_effect::NON_SCALING, "data-"].iter().any(|t| svg.contains(t)) {
         return (svg.into(), found);
     }
     let Ok(xml) = roxmltree::Document::parse_with_options(svg, roxmltree::ParsingOptions { allow_dtd: true, ..Default::default() }) else {
@@ -403,6 +409,14 @@ fn prepass<'s>(svg: &'s str, opts: &ImportOptions) -> (Cow<'s, str>, Found) {
             found.links.insert(edits.id(svg, a), url.to_string());
         }
     }
+    if svg.contains("data-") {
+        for e in elements().filter(|e| OBJECT_ELEMENTS.contains(&e.tag_name().name())) {
+            let data = user_data(e);
+            if !data.is_empty() {
+                found.data.insert(edits.id(svg, e), data);
+            }
+        }
+    }
     let symbols: HashSet<&str> = elements().filter(|n| n.tag_name().name() == "symbol").filter_map(|n| n.attribute("id")).collect();
     for u in elements().filter(|n| n.tag_name().name() == "use") {
         if let Some(sym) = href(u).and_then(|h| h.strip_prefix('#')).filter(|s| symbols.contains(s)) {
@@ -456,6 +470,24 @@ fn tag_name_end(svg: &str, n: XNode) -> usize {
     svg.get(start + 1..).and_then(|s| s.find(|c: char| c.is_whitespace() || c == '/' || c == '>')).map_or(start + 2, |i| start + 1 + i)
 }
 
+/// The elements that become objects, whose `data-*` attributes are kept.
+const OBJECT_ELEMENTS: &[&str] = &["g", "a", "use", "path", "rect", "circle", "ellipse", "line", "polyline", "polygon", "image"];
+
+/// The most `data-*` attributes kept per element (the file is untrusted).
+const MAX_DATA: usize = 64;
+
+/// The `data-*` attributes of element `e`, in order, without the `data-` (ours, `data-name` and
+/// `data-vc-*`, aside).
+fn user_data(e: XNode) -> Vec<(String, String)> {
+    e.attributes()
+        .filter(|a| a.namespace().is_none())
+        .filter_map(|a| Some((a.name().strip_prefix("data-")?, a.value())))
+        .filter(|(k, _)| !k.is_empty() && *k != "name" && !k.starts_with("vc-"))
+        .take(MAX_DATA)
+        .map(|(k, v)| (k.to_string(), v.to_string()))
+        .collect()
+}
+
 /// Make `n` link to `url`, unless it links somewhere already (an inner link wins).
 fn link(n: &mut Node, url: &str) {
     if n.url().is_none() {
@@ -592,9 +624,18 @@ impl Importer {
         if self.hidden.contains(n.id()) {
             out.visible = false;
         }
+        self.keep_data(n.id(), &mut out);
         Some(out)
     }
 
+    /// Give `n` the `data-*` attributes of element `id`, unless it has data already (what an
+    /// inner element made of it keeps).
+    fn keep_data(&self, id: &str, n: &mut Node) {
+        if let Some(data) = self.data.get(id).filter(|_| n.attrs.as_ref().is_none_or(|a| a.data.is_empty())) {
+            n.edit_attrs(|a| a.data = data.clone());
+        }
+    }
+
     /// A gradient's stops, midpoints restored.
     fn stops(&self, g: &usvg::BaseGradient) -> Vec<GradientStop> {
         gradient_stops(g, self.midpoints.get(g.id()).map(Vec::as_slice))
@@ -1114,9 +1155,10 @@ impl Importer {
             std::mem::take(&mut self.uses),
             std::mem::take(&mut self.labels),
             std::mem::take(&mut self.non_scaling),
+            std::mem::take(&mut self.data),
         );
         let art = self.group_node(tree.root(), acc);
-        (self.links, self.hidden, self.uses, self.labels, self.non_scaling) = outer;
+        (self.links, self.hidden, self.uses, self.labels, self.non_scaling, self.data) = outer;
         art
     }
 }

crates/svg/src/lib.rs

@@ -208,7 +208,8 @@ pub struct ExportOptions {
     /// One positioned `<tspan>` per line of type instead of one per style run, tab stop and
     /// justified word (smaller; viewers then space the line with their own font metrics).
     pub fewer_tspans: bool,
-    /// Keep hidden layers, written hidden (`display:none`), as Save does; exports leave them out.
+    /// Keep hidden layers and objects, written hidden (`display="none"`), as Save does; exports
+    /// leave them out unless asked.
     pub hidden_layers: bool,
     /// The file's character encoding (see [`Output::bytes`]).
     pub encoding: Encoding,

crates/svg/tests/symbols_layers.rs

@@ -1,6 +1,7 @@
 //! Symbols export as one `<symbol>` def and a `<use>` per instance (instances the def can't stand
-//! for get their own art), hidden layers are kept hidden when asked and come back hidden, clipped
-//! layers come in as clipping layers, and the editing data notices edits made elsewhere.
+//! for get their own art), hidden layers and objects are kept hidden when asked and come back
+//! hidden with their `data-*` attributes, clipped layers come in as clipping layers, and the
+//! editing data notices edits made elsewhere.
 // Integration tests: unwrapping and panicking on failure is fine here, unlike in shipped code (AGENTS.md › Robustness).
 #![allow(clippy::unwrap_used, clippy::expect_used, clippy::panic)]
 
@@ -205,6 +206,61 @@ fn hidden_layers_are_kept_hidden_when_asked() {
     }
 }
 
+/// An animation rig (#522): hidden alternates (a group and a lone path) and rotation pivots kept as
+/// `data-*` attributes.
+const RIG: &str = r##"<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 200 200" width="200" height="200">
+  <g id="character" data-pivot="100,180">
+    <g id="arm" data-pivot="60,100" data-z-order="2"><path d="M40 100 L60 90 L80 110 Z" fill="#b5835a"/></g>
+    <g id="arm-raised" data-pivot="60,100" display="none"><path d="M40 100 L50 60 L70 70 Z" fill="#b5835a"/></g>
+    <path id="eye-closed" d="M90 80 L110 80 L100 95 Z" fill="#000" style="display:none" data-blink="1"/>
+  </g>
+</svg>"##;
+
+/// The `data-*` attributes of the object named `name`.
+fn data_of(d: &Document, name: &str) -> Vec<(String, String)> {
+    let mut found = vec![];
+    d.walk(|n| {
+        if n.name.as_deref() == Some(name) {
+            found = n.attrs.as_deref().map(|a| a.data.clone()).unwrap_or_default();
+        }
+    });
+    found
+}
+
+#[test]
+fn hidden_objects_and_data_attributes_round_trip() {
+    let d = import(RIG).unwrap();
+    let pivot = |v: &str| vec![("pivot".to_string(), v.to_string())];
+    assert_eq!(data_of(&d, "character"), pivot("100,180"));
+    assert_eq!(data_of(&d, "arm"), [("pivot".to_string(), "60,100".to_string()), ("z-order".to_string(), "2".to_string())]);
+    assert_eq!(data_of(&d, "arm-raised"), pivot("60,100"));
+    let hidden = |d: &Document| {
+        let mut v = vec![];
+        d.walk(|n| {
+            if !n.visible {
+                v.push(n.name.clone().unwrap_or_default());
+            }
+        });
+        v
+    };
+    assert_eq!(hidden(&d), ["arm-raised", "eye-closed"]);
+    // An export leaves the hidden objects out, their data with them; the others keep theirs.
+    let plain = export(&d, &ExportOptions::default());
+    assert!(!plain.contains("arm-raised") && !plain.contains("eye-closed") && plain.contains("data-pivot=\"60,100\""), "{plain}");
+    let styles = [vectorcraft_svg::Styling::PresentationAttributes, vectorcraft_svg::Styling::InlineStyle, vectorcraft_svg::Styling::InternalCss];
+    for styling in styles {
+        // Kept (Save, or asked), they are written hidden and come back hidden, with every attribute.
+        let kept = export(&d, &ExportOptions { hidden_layers: true, styling, ..Default::default() });
+        assert!(kept.contains("data-pivot=\"100,180\"") && kept.contains("data-z-order=\"2\"") && kept.contains("data-blink=\"1\""), "{kept}");
+        assert_eq!(resvg_render(&kept, 200, 200).pixel(100, 85), [255, 255, 255, 255], "hidden, not drawn: {kept}");
+        let back = import(&kept).unwrap();
+        assert_eq!(hidden(&back), ["arm-raised", "eye-closed"], "{kept}");
+        for name in ["character", "arm", "arm-raised", "eye-closed"] {
+            assert_eq!(data_of(&back, name), data_of(&d, name), "{name}: {kept}");
+        }
+    }
+}
+
 /// Each layer's art: clipping layer or not, and the kinds of its children.
 fn layer_art(d: &Document) -> Vec<(String, bool, Vec<&'static str>)> {
     d.layers.iter().map(|l| (l.name.clone().unwrap_or_default(), l.clips(), l.children().unwrap().iter().map(|c| c.kind_label()).collect())).collect()

docs/mcp.md

@@ -266,9 +266,10 @@ place and paste). `run_command document.save {path: "x.svg", svg: {…}}` saves
 Symbols export as one `<symbol>` with a `<use>` per instance. An instance the def can't stand for is written as its
 own art: one stained by its fill; one scaled while the symbol has strokes (their weight doesn't scale), or rotated or
 scaled while it has effects, brushes or live objects; and every instance of a symbol with pattern paints or unlinked
-opacity masks (those stay on the page). `hiddenLayers: true` keeps hidden layers as groups that aren't displayed
-(`display:none`); `document.save` keeps them unless told otherwise, exports leave them out, and they reopen as
-hidden layers. A `preserveEditing` SVG carries the native document (CDATA in `<metadata>`) and a hash of the
+opacity masks (those stay on the page). `hiddenLayers: true` keeps hidden layers and objects, not displayed
+(`display="none"`); `document.save` and the CLI's `convert` keep them unless told otherwise, other exports leave
+them out, and they reopen hidden. An object's own data (`object.setProps {data: {pivot: "100,180"}}`) is written as
+`data-*` attributes (`data-pivot="100,180"`), and an SVG's `data-*` attributes come in as it. A `preserveEditing` SVG carries the native document (CDATA in `<metadata>`) and a hash of the
 markup around it: if another app changed the SVG since, `document.open` reads it as plain SVG and says so in
 `warnings`.