diff --git a/crates/cad/src/import.rs b/crates/cad/src/import.rs
index b7967093..f1f41048 100644
--- a/crates/cad/src/import.rs
+++ b/crates/cad/src/import.rs
@@ -214,6 +214,7 @@ pub fn import(bytes: &[u8], o: &ImportOptions) -> Result<Imported, String> {
     let (mut document, mut warnings) = build::Build::new(&d, o).run(layout, natural, ratio)?;
     document.units = if o.fit { unit } else { o.unit.unwrap_or(unit) };
     warnings.extend(damaged);
+    document.limit_depth_noting(&mut warnings);
     Ok(Imported { document, warnings })
 }
 
diff --git a/crates/doc/src/clipnest.rs b/crates/doc/src/clipnest.rs
index 64d5c3f4..f77f9e01 100644
--- a/crates/doc/src/clipnest.rs
+++ b/crates/doc/src/clipnest.rs
@@ -24,8 +24,10 @@ pub struct Clip {
 }
 
 /// Deepest nesting of clips, and of groups, an importer records ([`nest`] goes one level deeper
-/// for each): deeper ones are left out.
-pub const MAX_NEST: usize = 128;
+/// for each): deeper ones are left out. As deep as a document's objects may nest
+/// ([`crate::MAX_DEPTH`]) under a layer, around the art; clips in groups that deep together are
+/// merged by [`Document::limit_depth`].
+pub const MAX_NEST: usize = crate::MAX_DEPTH - 2;
 
 /// The warning for clips left out for nesting deeper than [`MAX_NEST`].
 pub fn deep_clips() -> String {
diff --git a/crates/doc/src/depth.rs b/crates/doc/src/depth.rs
new file mode 100644
index 00000000..464eaf9d
--- /dev/null
+++ b/crates/doc/src/depth.rs
@@ -0,0 +1,588 @@
+//! How deep objects may nest.
+//!
+//! The tree is walked by recursion everywhere (drawing, bounds, hit tests, saving, exporting), so
+//! a tree of unbounded depth overflows the stack: an abort no guard catches. No document deeper
+//! than [`MAX_DEPTH`] is ever kept, nor one whose symbols and patterns draw deeper than
+//! [`MAX_DRAWN_DEPTH`] (a symbol holding an instance of itself, or a pattern painting its own
+//! tile, draws without end): importers and the native reader merge deeper objects into the group
+//! around them and leave such instances and paints out
+//! ([`Document::limit_depth`], with [`merged_note`] and [`symbols_note`] as their warnings), and
+//! the engine refuses an edit that would nest deeper ([`Document::too_deep`]).
+
+use std::collections::HashMap;
+use std::sync::Arc;
+
+use vectorcraft_color::Paint;
+
+use crate::{Document, Node, NodeKind};
+
+/// The deepest an object may be: a top-level layer is 1 deep, what it holds 2, and so on (the art
+/// of an opacity mask is one deeper than the object it masks). A symbol's or pattern's art counts
+/// from 1 again.
+///
+/// A native file writes three levels of JSON for each level of objects, and its reader stops at
+/// 128 levels: 32 leaves the deepest object 29 of them for its own data, so every document that
+/// can be made can be saved and opened again.
+pub const MAX_DEPTH: usize = 32;
+
+/// The deepest an object may be drawn: as [`MAX_DEPTH`], the art of a symbol counted under its
+/// instance and a pattern's tile under the object it paints (and what those use, under them).
+/// Symbols a few objects deep nest in one another dozens deep within it.
+pub const MAX_DRAWN_DEPTH: usize = 4 * MAX_DEPTH;
+
+/// The warning of a file whose objects were nested deeper than [`MAX_DEPTH`].
+pub fn merged_note() -> String {
+    format!("objects nested more than {MAX_DEPTH} deep were merged into the group around them")
+}
+
+/// The warning of a file with symbols or patterns that use themselves or are drawn deeper than
+/// [`MAX_DRAWN_DEPTH`].
+pub fn symbols_note() -> String {
+    format!(
+        "symbol instances and pattern paints inside their own symbol or pattern, or drawn more than {MAX_DRAWN_DEPTH} objects deep, were left out"
+    )
+}
+
+/// Run `f` where recursion has room: on a thread of its own with a 16 MB stack (the main thread
+/// has 1 MB on Windows), or here where there are no threads (the web) or none can be started. For
+/// readers whose recursion is capped but heavy; a panic in `f` goes on to the caller.
+pub fn with_deep_stack<T: Send>(f: impl Fn() -> T + Sync) -> T {
+    #[cfg(not(target_arch = "wasm32"))]
+    {
+        let threaded = std::thread::scope(|s| {
+            let thread = std::thread::Builder::new().stack_size(16 << 20).spawn_scoped(s, &f).ok()?;
+            Some(thread.join().unwrap_or_else(|panic| std::panic::resume_unwind(panic)))
+        });
+        if let Some(done) = threaded {
+            return done;
+        }
+    }
+    f()
+}
+
+/// Is anything in `now` (each `depth` deep) deeper than [`MAX_DEPTH`], or `over` (given its
+/// depth)? Without recursion: the trees may be of any depth. With `before` (the same list before
+/// an edit, within the caps), only what the edit changed is looked at: a subtree still shared with
+/// it, in the same place, is as it was.
+fn deeper(now: &[Arc<Node>], before: Option<&[Arc<Node>]>, depth: usize, over: &dyn Fn(&Node, usize) -> bool) -> bool {
+    type Pending<'a> = Vec<(&'a Node, Option<&'a Node>, usize)>;
+    fn push<'a>(stack: &mut Pending<'a>, now: &'a [Arc<Node>], before: Option<&'a [Arc<Node>]>, depth: usize) {
+        for (i, n) in now.iter().enumerate() {
+            let was = before.and_then(|b| b.get(i));
+            if !was.is_some_and(|w| Arc::ptr_eq(w, n)) {
+                stack.push((n, was.map(|w| &**w), depth));
+            }
+        }
+    }
+    let mut stack = vec![];
+    push(&mut stack, now, before, depth);
+    while let Some((n, was, d)) = stack.pop() {
+        if d > MAX_DEPTH || over(n, d) {
+            return true;
+        }
+        if let Some(ch) = n.children() {
+            push(&mut stack, ch, was.and_then(Node::children).map(Vec::as_slice), d + 1);
+        }
+        if let Some(m) = &n.extras().mask {
+            let was = was.and_then(|w| w.extras().mask.as_ref()).map(|m| std::slice::from_ref(&m.art));
+            push(&mut stack, std::slice::from_ref(&m.art), was, d + 1);
+        }
+    }
+    false
+}
+
+/// [`deeper`] for the nesting alone.
+fn nested_deeper(now: &[Arc<Node>], depth: usize) -> bool {
+    deeper(now, None, depth, &|_, _| false)
+}
+
+/// Merge what is deeper than [`MAX_DEPTH`] in `nodes` (each `depth` deep) into the group around
+/// it: a container at the cap is replaced by what it holds (a clipping group's clipping path and
+/// an opacity mask too deep are left out); what it held stays hidden or locked as it was. Returns
+/// whether anything changed. Recurses no deeper than the cap.
+fn limit(nodes: &mut Vec<Arc<Node>>, depth: usize) -> bool {
+    let mut changed = false;
+    let mut i = 0;
+    while let Some(n) = nodes.get_mut(i) {
+        if !nested_deeper(std::slice::from_ref(n), depth) {
+            i += 1;
+            continue;
+        }
+        changed = true;
+        let n = Arc::make_mut(n);
+        if n.extras().mask.as_ref().is_some_and(|m| nested_deeper(std::slice::from_ref(&m.art), depth + 1)) {
+            n.extras_mut().mask = None;
+        }
+        if depth < MAX_DEPTH {
+            if let Some(ch) = n.children_mut() {
+                limit(ch, depth + 1);
+            }
+            i += 1;
+            continue;
+        }
+        let clip = matches!(n.kind, NodeKind::Group { clip: true, .. } | NodeKind::Layer { clip: true, .. });
+        let (visible, locked) = (n.visible, n.locked);
+        let mut held = n.children_mut().map(std::mem::take).unwrap_or_default();
+        if clip && !held.is_empty() {
+            held.remove(0);
+        }
+        for c in &mut held {
+            if (!visible && c.visible) || (locked && !c.locked) {
+                let c = Arc::make_mut(c);
+                c.visible &= visible;
+                c.locked |= locked;
+            }
+        }
+        // What it held takes its place, and is looked at in its turn.
+        nodes.splice(i..=i, held);
+    }
+    changed
+}
+
+/// A symbol (`false`) or a pattern (`true`) of the document, by name: what art draws by name, an
+/// instance its symbol's art and a pattern paint its tile's.
+type Def<'a> = (bool, &'a str);
+
+/// How deep each symbol's and pattern's art is drawn, the art of the symbols and patterns it uses
+/// included (drawn under the object that uses them): `None` for one that uses itself, in its art
+/// or through what that uses, or is drawn deeper than [`MAX_DRAWN_DEPTH`].
+type Heights<'a> = HashMap<Def<'a>, Option<usize>>;
+
+/// What `n` itself draws by name: the symbol it is an instance of, the patterns that paint it.
+fn uses(n: &Node) -> impl Iterator<Item = Def<'_>> {
+    let symbol = match &n.kind {
+        NodeKind::SymbolInstance { symbol, .. } => Some((false, symbol.as_str())),
+        _ => None,
+    };
+    let patterns = crate::swatches::node_paints(n).filter_map(|p| match p {
+        Paint::Pattern { pattern, .. } => Some((true, pattern.as_str())),
+        _ => None,
+    });
+    symbol.into_iter().chain(patterns)
+}
+
+/// [`Heights`] of the document's symbols and patterns. Without recursion: they may use one
+/// another in a chain of any length. Their own art is within [`MAX_DEPTH`].
+fn heights(doc: &Document) -> Heights<'_> {
+    // Each one's own depth, and what its art uses with the deepest use of each.
+    type Own<'a> = (usize, Vec<(Def<'a>, usize)>);
+    let arts = (doc.symbols.iter().map(|s| ((false, s.name.as_str()), std::slice::from_ref(&s.art))))
+        .chain(doc.patterns.iter().map(|p| ((true, p.name.as_str()), &p.art[..])));
+    let mut own: HashMap<Def, Own> = HashMap::new();
+    for (def, art) in arts {
+        let (mut deepest, mut used) = (0, HashMap::<Def, usize>::new());
+        let mut stack: Vec<(&Node, usize)> = art.iter().map(|n| (&**n, 1)).collect();
+        while let Some((n, d)) = stack.pop() {
+            deepest = deepest.max(d);
+            for u in uses(n) {
+                let at = used.entry(u).or_default();
+                *at = (*at).max(d);
+            }
+            stack.extend(n.children().into_iter().flatten().chain(n.extras().mask.as_ref().map(|m| &m.art)).map(|c| (&**c, d + 1)));
+        }
+        // (The first of two of one name is the one drawn.)
+        own.entry(def).or_insert((deepest, used.into_iter().collect()));
+    }
+    // Depth first over what uses what. One met again while it is being worked out (`None` in its
+    // entry) uses itself.
+    let mut found: HashMap<Def, Option<Option<usize>>> = HashMap::new();
+    let starts: Vec<Def> = own.keys().copied().collect();
+    for start in starts {
+        if found.contains_key(&start) {
+            continue;
+        }
+        // (which, the next of its uses to look at, the deepest found so far: `None` once it can't be drawn)
+        let mut path: Vec<(Def, usize, Option<usize>)> = vec![(start, 0, own.get(&start).map(|o| o.0))];
+        found.insert(start, None);
+        while let Some(&(def, next, deepest)) = path.last() {
+            let used = own.get(&def).map_or(&[][..], |o| &o.1);
+            let Some(&(other, at)) = used.get(next) else {
+                // Everything it uses is worked out.
+                let deepest = deepest.filter(|d| *d <= MAX_DRAWN_DEPTH);
+                found.insert(def, Some(deepest));
+                path.pop();
+                if let Some((user, next, held)) = path.last_mut() {
+                    let at = own.get(user).and_then(|o| o.1.get(next.wrapping_sub(1))).map_or(1, |u| u.1);
+                    *held = held.zip(deepest).map(|(h, d)| h.max(at + d));
+                }
+                continue;
+            };
+            let known = found.get(&other).copied();
+            if known.is_none() && own.contains_key(&other) {
+                found.insert(other, None);
+            }
+            let Some((_, next, deepest)) = path.last_mut() else { break };
+            *next += 1;
+            match known {
+                // Not in the document: it draws nothing.
+                None if !own.contains_key(&other) => {}
+                None => path.push((other, 0, own.get(&other).map(|o| o.0))),
+                Some(Some(Some(d))) => *deepest = deepest.map(|h| h.max(at + d)),
+                // It uses itself (it is on the way down here), or can't be drawn.
+                Some(None | Some(None)) => *deepest = None,
+            }
+        }
+    }
+    found.into_iter().map(|(def, h)| (def, h.flatten())).collect()
+}
+
+/// Can't `used`, by an object `depth` deep, be drawn there?
+fn undrawable(heights: &Heights, used: Def, depth: usize) -> bool {
+    heights.get(&used).is_some_and(|h| h.is_none_or(|h| depth + h > MAX_DRAWN_DEPTH))
+}
+
+/// Take out of `nodes` (each `depth` deep) the uses `bad` picks (given the depth of the object):
+/// an instance goes, a pattern paint becomes no paint. Returns whether anything changed. For trees
+/// within [`MAX_DEPTH`].
+fn strip(nodes: &mut Vec<Arc<Node>>, depth: usize, bad: &dyn Fn(Def, usize) -> bool) -> bool {
+    let any = |n: &Node, d: usize| uses(n).any(|u| bad(u, d));
+    let before = nodes.len();
+    nodes.retain(|n| !matches!(&n.kind, NodeKind::SymbolInstance { symbol, .. } if bad((false, symbol.as_str()), depth)));
+    let mut changed = nodes.len() != before;
+    for n in nodes.iter_mut() {
+        if !deeper(std::slice::from_ref(n), None, depth, &any) {
+            continue;
+        }
+        changed = true;
+        let n = Arc::make_mut(n);
+        if uses(n).any(|u| bad(u, depth)) {
+            for p in crate::swatches::node_paints_mut(n) {
+                if matches!(p, Paint::Pattern { pattern, .. } if bad((true, pattern.as_str()), depth)) {
+                    *p = Paint::None;
+                }
+            }
+        }
+        // An opacity mask whose art is such an instance goes with it.
+        let mut mask = n.extras().mask.as_ref().map(|m| vec![m.art.clone()]);
+        if let Some(art) = &mut mask
+            && strip(art, depth + 1, bad)
+        {
+            match art.pop() {
+                Some(art) => {
+                    if let Some(m) = n.extras_mut().mask.as_mut() {
+                        m.art = art;
+                    }
+                }
+                None => n.extras_mut().mask = None,
+            }
+        }
+        if let Some(ch) = n.children_mut() {
+            strip(ch, depth + 1, bad);
+        }
+    }
+    changed
+}
+
+impl Document {
+    /// Is anything nested deeper than [`MAX_DEPTH`], or drawn deeper than [`MAX_DRAWN_DEPTH`]
+    /// (a symbol or pattern that uses itself is)? With `before` (this document before an edit,
+    /// itself within the caps), only what the edit changed is looked at.
+    pub fn too_deep(&self, before: Option<&Document>) -> bool {
+        fn symbol(d: &Document, i: usize) -> Option<&[Arc<Node>]> {
+            d.symbols.get(i).map(|s| std::slice::from_ref(&s.art))
+        }
+        fn pattern(d: &Document, i: usize) -> Option<&[Arc<Node>]> {
+            d.patterns.get(i).map(|p| &p.art[..])
+        }
+        let nested = |_: &Node, _: usize| false;
+        if (0..self.symbols.len()).any(|i| symbol(self, i).is_some_and(|art| deeper(art, before.and_then(|b| symbol(b, i)), 1, &nested)))
+            || (0..self.patterns.len()).any(|i| pattern(self, i).is_some_and(|art| deeper(art, before.and_then(|b| pattern(b, i)), 1, &nested)))
+        {
+            return true;
+        }
+        if self.symbols.is_empty() && self.patterns.is_empty() {
+            return deeper(&self.layers, before.map(|b| &b.layers[..]), 1, &nested);
+        }
+        let heights = heights(self);
+        if heights.values().any(Option::is_none) {
+            return true;
+        }
+        // Symbols and patterns draw as deep as before when none changed; else every use of them
+        // is looked at again.
+        let same = |x: &[Arc<Node>], y: &[Arc<Node>]| x.len() == y.len() && x.iter().zip(y).all(|(x, y)| Arc::ptr_eq(x, y));
+        let before = before.filter(|b| {
+            b.symbols.len() == self.symbols.len()
+                && b.patterns.len() == self.patterns.len()
+                && b.symbols.iter().zip(&self.symbols).all(|(x, y)| x.name == y.name && Arc::ptr_eq(&x.art, &y.art))
+                && b.patterns.iter().zip(&self.patterns).all(|(x, y)| x.name == y.name && same(&x.art, &y.art))
+        });
+        let over = |n: &Node, d: usize| uses(n).any(|u| undrawable(&heights, u, d));
+        deeper(&self.layers, before.map(|b| &b.layers[..]), 1, &over)
+    }
+
+    /// [`Self::limit_depth`] → whether objects were merged, and whether uses of symbols and
+    /// patterns were left out.
+    fn limit_depths(&mut self) -> (bool, bool) {
+        let mut merged = limit(&mut self.layers, 1);
+        for s in &mut self.symbols {
+            // The art itself is 1 deep, so it stays the one object it is.
+            let mut art = vec![s.art.clone()];
+            if limit(&mut art, 1)
+                && let Some(one) = art.pop()
+            {
+                s.art = one;
+                merged = true;
+            }
+        }
+        for p in &mut self.patterns {
+            merged |= limit(&mut p.art, 1);
+        }
+        if self.symbols.is_empty() && self.patterns.is_empty() {
+            return (merged, false);
+        }
+        // The symbols and patterns that can't be drawn lose what their art uses: each is then as
+        // deep as its own art, and what uses it can be drawn.
+        let (symbols, patterns): (Vec<usize>, Vec<usize>) = {
+            let heights = heights(self);
+            let bad = |def: Def| heights.get(&def).is_some_and(Option::is_none);
+            (
+                (0..self.symbols.len()).filter(|i| self.symbols.get(*i).is_some_and(|s| bad((false, s.name.as_str())))).collect(),
+                (0..self.patterns.len()).filter(|i| self.patterns.get(*i).is_some_and(|p| bad((true, p.name.as_str())))).collect(),
+            )
+        };
+        let mut left_out = !(symbols.is_empty() && patterns.is_empty());
+        let all = |_: Def, _: usize| true;
+        for i in symbols {
+            let Some(s) = self.symbols.get_mut(i) else { continue };
+            let mut art = vec![s.art.clone()];
+            strip(&mut art, 1, &all);
+            // (An instance alone was the whole art: an empty group stands in.)
+            s.art = art.pop().unwrap_or_else(|| Arc::new(Node::group(s.art.id, vec![])));
+        }
+        for i in patterns {
+            if let Some(p) = self.patterns.get_mut(i) {
+                strip(&mut p.art, 1, &all);
+            }
+        }
+        // Then the uses drawn too deep where they are.
+        let mut layers = self.layers.clone();
+        left_out |= {
+            let heights = heights(self);
+            strip(&mut layers, 1, &|used, depth| undrawable(&heights, used, depth))
+        };
+        self.layers = layers;
+        (merged, left_out)
+    }
+
+    /// Bring the document within the caps: merge the objects nested deeper than [`MAX_DEPTH`]
+    /// into the group around them, and leave out the uses of symbols and patterns that can't be
+    /// drawn (inside their own symbol or pattern, or deeper than [`MAX_DRAWN_DEPTH`]). What an
+    /// importer does to what it read. Returns whether anything changed.
+    pub fn limit_depth(&mut self) -> bool {
+        let (merged, left_out) = self.limit_depths();
+        merged || left_out
+    }
+
+    /// [`Self::limit_depth`], adding [`merged_note`] and [`symbols_note`] to an importer's
+    /// `warnings` for what it did.
+    pub fn limit_depth_noting(&mut self, warnings: &mut Vec<String>) {
+        let (merged, left_out) = self.limit_depths();
+        warnings.extend(merged.then(merged_note));
+        warnings.extend(left_out.then(symbols_note));
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{NodeId, OpacityMask};
+
+    /// One path in `levels` groups, each holding a second path beside the next group.
+    fn nested(levels: usize) -> Arc<Node> {
+        let mut id = 0;
+        let mut next = || {
+            id += 1;
+            NodeId(id)
+        };
+        let path = |id| Arc::new(Node::path(id, Default::default(), Default::default()));
+        let mut inner = path(next());
+        for _ in 0..levels {
+            inner = Arc::new(Node::group(next(), vec![inner, path(next())]));
+        }
+        inner
+    }
+
+    fn doc(art: Arc<Node>) -> Document {
+        let mut d = Document::new(100.0, 100.0);
+        if let Some(ch) = d.layers.first_mut().and_then(|l| Arc::make_mut(l).children_mut()) {
+            ch.push(art);
+        }
+        d
+    }
+
+    #[test]
+    fn a_document_at_the_cap_is_left_alone() {
+        // The layer, the groups and the path in them: MAX_DEPTH deep.
+        let mut d = doc(nested(MAX_DEPTH - 2));
+        let before = d.clone();
+        assert!(!d.too_deep(None));
+        assert!(!d.limit_depth());
+        assert_eq!(d, before);
+    }
+
+    #[test]
+    fn deeper_objects_are_merged_into_the_group_around_them() {
+        for levels in [MAX_DEPTH - 1, MAX_DEPTH + 5, 100_000] {
+            let mut d = doc(nested(levels));
+            assert!(d.too_deep(None), "{levels}");
+            assert!(d.limit_depth(), "{levels}");
+            assert!(!d.too_deep(None), "{levels}");
+            // Every path is kept, under the layer and the groups down to the cap.
+            assert_eq!(d.node_count(), 1 + (MAX_DEPTH - 2) + (levels + 1), "{levels}");
+            assert!(!d.limit_depth(), "nothing more to merge");
+        }
+    }
+
+    #[test]
+    fn a_clipping_path_and_a_mask_too_deep_are_left_out_and_hidden_art_stays_hidden() {
+        let mut inner = Node::new(NodeId(9000), NodeKind::Group { children: vec![nested(0), nested(0)], clip: true });
+        inner.visible = false;
+        let mut art = Arc::new(inner);
+        for i in 0..MAX_DEPTH {
+            art = Arc::new(Node::group(NodeId(9001 + i as u64), vec![art]));
+        }
+        let mut masked = Node::group(NodeId(8000), vec![]);
+        masked.extras_mut().mask = Some(Box::new(OpacityMask::new((*nested(MAX_DEPTH)).clone(), true)));
+        let mut d = doc(art);
+        if let Some(ch) = d.layers.first_mut().and_then(|l| Arc::make_mut(l).children_mut()) {
+            ch.push(Arc::new(masked));
+        }
+        assert!(d.limit_depth());
+        assert!(!d.too_deep(None));
+        let mut leaves = vec![];
+        d.walk(|n| {
+            if n.children().is_none() {
+                leaves.push(n.visible);
+            }
+        });
+        assert_eq!(leaves, [false], "the clipping path is gone, what it clipped is still hidden");
+        assert!(d.node(NodeId(8000)).is_some_and(|n| n.extras().mask.is_none()));
+    }
+
+    #[test]
+    fn an_edit_is_checked_by_what_it_changed() {
+        let before = doc(nested(MAX_DEPTH - 2));
+        let mut wrapped = before.clone();
+        if let Some(ch) = wrapped.layers.first_mut().and_then(|l| Arc::make_mut(l).children_mut()) {
+            let all = std::mem::take(ch);
+            ch.push(Arc::new(Node::group(NodeId(7000), all)));
+        }
+        assert!(wrapped.too_deep(Some(&before)), "the same art, one deeper");
+        let mut beside = before.clone();
+        if let Some(ch) = beside.layers.first_mut().and_then(|l| Arc::make_mut(l).children_mut()) {
+            ch.push(nested(3));
+        }
+        assert!(!beside.too_deep(Some(&before)));
+        assert!(!before.too_deep(Some(&before)));
+    }
+
+    #[test]
+    fn symbols_and_patterns_are_limited_too() {
+        let mut d = Document::new(10.0, 10.0);
+        d.symbols.push(crate::Symbol { name: "s".into(), art: nested(MAX_DEPTH + 3) });
+        assert!(d.too_deep(None));
+        assert!(d.limit_depth());
+        assert!(!d.too_deep(None));
+        assert!(d.symbols.first().is_some_and(|s| s.art.children().is_some()), "still one object");
+    }
+
+    fn instance(id: u64, of: &str) -> Arc<Node> {
+        Arc::new(Node::new(NodeId(id), NodeKind::SymbolInstance { symbol: of.into(), xf: Default::default() }))
+    }
+
+    /// `count` symbols, each `levels` groups around an instance of the next; the last one's of `last`.
+    fn symbols(count: usize, levels: usize, last: &str) -> Document {
+        let mut d = doc(instance(1, "s0"));
+        for i in 0..count {
+            let mut art = instance(2, &if i + 1 < count { format!("s{}", i + 1) } else { last.to_string() });
+            for _ in 0..levels {
+                art = Arc::new(Node::group(NodeId(3), vec![art]));
+            }
+            d.symbols.push(crate::Symbol { name: format!("s{i}"), art });
+        }
+        d
+    }
+
+    fn instances(d: &Document) -> usize {
+        let mut n = 0;
+        let mut count = |x: &Node| n += usize::from(matches!(x.kind, NodeKind::SymbolInstance { .. }));
+        d.walk(&mut count);
+        d.symbols.iter().for_each(|s| s.art.walk(&mut count));
+        n
+    }
+
+    #[test]
+    fn symbols_in_symbols_are_drawn_only_so_deep() {
+        // Three objects deep each (two groups and the instance), under the instance on the layer.
+        let fits = MAX_DRAWN_DEPTH / 3 - 1;
+        let mut d = symbols(fits, 2, "none");
+        assert!(!d.too_deep(None) && !d.limit_depth());
+        let mut d = symbols(fits + 2, 2, "none");
+        assert!(d.too_deep(None));
+        let before = instances(&d);
+        assert!(d.limit_depth() && !d.too_deep(None));
+        assert!(instances(&d) < before && instances(&d) > 0, "only the instances drawn too deep go");
+        // A chain of any length is measured, not walked by recursion.
+        let mut d = symbols(100_000, 0, "none");
+        assert!(d.too_deep(None) && d.limit_depth() && !d.too_deep(None));
+    }
+
+    #[test]
+    fn a_symbol_holding_itself_loses_the_instance() {
+        for (count, last) in [(1, "s0"), (3, "s0"), (3, "s1")] {
+            let mut d = symbols(count, 1, last);
+            assert!(d.too_deep(None), "{count} {last}");
+            let mut warnings = vec![];
+            d.limit_depth_noting(&mut warnings);
+            assert_eq!(warnings, [symbols_note()]);
+            assert!(!d.too_deep(None), "{count} {last}");
+            assert!(d.symbols.iter().all(|s| s.art.children().is_some()), "the art is still a group");
+        }
+        // An edit that makes one hold itself is seen, whatever else stayed as it was.
+        let before = symbols(2, 1, "none");
+        let mut after = before.clone();
+        after.symbols[1].art = Arc::new(Node::group(NodeId(9), vec![instance(8, "s0")]));
+        assert!(!before.too_deep(None) && after.too_deep(Some(&before)));
+    }
+
+    /// A path painted with the pattern named `with`.
+    fn painted(id: u64, with: &str) -> Arc<Node> {
+        let fill = Paint::Pattern { pattern: with.into(), xf: Default::default() };
+        Arc::new(Node::path(NodeId(id), Default::default(), crate::Appearance::basic(fill, Paint::None, 0.0)))
+    }
+
+    fn pattern_fills(d: &Document) -> usize {
+        let mut n = 0;
+        d.visit_paints(&mut |p| n += usize::from(matches!(p, Paint::Pattern { .. })));
+        n
+    }
+
+    #[test]
+    fn a_pattern_painting_its_own_tile_loses_the_paint() {
+        // One that paints its own tile; two that paint each other's; one in a symbol it holds.
+        let itself = |d: &mut Document| d.patterns.push(crate::PatternDef::new("p", vec![painted(2, "p")]));
+        let each_other = |d: &mut Document| {
+            d.patterns.push(crate::PatternDef::new("p", vec![painted(2, "q")]));
+            d.patterns.push(crate::PatternDef::new("q", vec![painted(3, "p")]));
+        };
+        let through_a_symbol = |d: &mut Document| {
+            d.patterns.push(crate::PatternDef::new("p", vec![instance(2, "s")]));
+            d.symbols.push(crate::Symbol { name: "s".into(), art: painted(3, "p") });
+        };
+        for make in [&itself as &dyn Fn(&mut Document), &each_other, &through_a_symbol] {
+            let mut d = doc(painted(1, "p"));
+            make(&mut d);
+            assert!(d.too_deep(None));
+            let mut warnings = vec![];
+            d.limit_depth_noting(&mut warnings);
+            assert_eq!(warnings, [symbols_note()]);
+            assert!(!d.too_deep(None));
+            assert_eq!(pattern_fills(&d), 1, "the object on the layer keeps its pattern");
+        }
+        // A pattern whose tile is painted with another is fine.
+        let mut d = doc(painted(1, "p"));
+        d.patterns.push(crate::PatternDef::new("p", vec![painted(2, "q")]));
+        d.patterns.push(crate::PatternDef::new("q", vec![painted(3, "none")]));
+        assert!(!d.too_deep(None) && !d.limit_depth());
+    }
+}
diff --git a/crates/doc/src/lib.rs b/crates/doc/src/lib.rs
index 1d4805ec..54af60a9 100644
--- a/crates/doc/src/lib.rs
+++ b/crates/doc/src/lib.rs
@@ -11,6 +11,7 @@ pub mod blend;
 pub mod clipnest;
 pub mod cmyk;
 pub mod corners;
+pub mod depth;
 pub mod graph;
 pub mod hit;
 mod id_index;
@@ -79,6 +80,7 @@ pub use appearance::{
 };
 pub use assets::ExportAsset;
 pub use corners::LiveCorners;
+pub use depth::MAX_DEPTH;
 pub use graph::{
     GraphDesign, GraphKind, GraphSpec, LabelStyles, MAX_GRAPH_CATEGORIES, MAX_GRAPH_SERIES, PiePosition, PieSort, SeriesPaint, TickLength,
     ValueAxisSide,
diff --git a/crates/doc/src/swatches.rs b/crates/doc/src/swatches.rs
index ab888d7f..bda2f47a 100644
--- a/crates/doc/src/swatches.rs
+++ b/crates/doc/src/swatches.rs
@@ -224,7 +224,7 @@ fn item_paint_mut(it: &mut AppearanceItem) -> &mut Paint {
 }
 
 /// The paints a node holds itself (not its children): appearance items, then text runs.
-fn node_paints(n: &Node) -> impl Iterator<Item = &Paint> {
+pub(crate) fn node_paints(n: &Node) -> impl Iterator<Item = &Paint> {
     let runs = match &n.kind {
         NodeKind::Text(t) => t.runs.as_slice(),
         _ => &[],
@@ -233,7 +233,7 @@ fn node_paints(n: &Node) -> impl Iterator<Item = &Paint> {
 }
 
 /// Mutable [`node_paints`], in the same order.
-fn node_paints_mut(n: &mut Node) -> impl Iterator<Item = &mut Paint> {
+pub(crate) fn node_paints_mut(n: &mut Node) -> impl Iterator<Item = &mut Paint> {
     let runs = match &mut n.kind {
         NodeKind::Text(t) => t.runs.as_mut_slice(),
         _ => &mut [],
diff --git a/crates/engine/src/cmd/fileio/affinity.rs b/crates/engine/src/cmd/fileio/affinity.rs
index 62311ed2..0a5a2f03 100644
--- a/crates/engine/src/cmd/fileio/affinity.rs
+++ b/crates/engine/src/cmd/fileio/affinity.rs
@@ -32,6 +32,7 @@ pub(super) fn import(name: &str, bytes: &[u8]) -> Result<Imported> {
         Ok(d) => {
             let mut b = Builder { doc: Document::new(0.0, 0.0), warnings: Vec::new(), k: 72.0 / d.dpi, layer: 0 };
             b.document(&d)?;
+            b.doc.limit_depth_noting(&mut b.warnings);
             let mut warnings = d.warnings.iter().map(|w| format!("Affinity: not imported or approximated: {w}.")).collect::<Vec<_>>();
             warnings.extend(b.warnings.iter().map(|w| format!("Affinity: {w}.")));
             Ok(Imported { doc: b.doc, warnings, preview_only: false })
diff --git a/crates/engine/src/cmd/fileio/load.rs b/crates/engine/src/cmd/fileio/load.rs
index f69f4c54..1ac08df1 100644
--- a/crates/engine/src/cmd/fileio/load.rs
+++ b/crates/engine/src/cmd/fileio/load.rs
@@ -139,7 +139,8 @@ fn restore_or_import(
 /// (with a warning for each that can't be used).
 pub(crate) fn native_file(bytes: &[u8]) -> Result<(Document, vectorcraft_format::FileInfo, Vec<String>)> {
     let f = vectorcraft_format::load_file(bytes).map_err(err)?;
-    let warnings = super::native::install_profiles(f.profiles);
+    let mut warnings = super::native::install_profiles(f.profiles);
+    warnings.extend(f.depth_notes);
     Ok((f.doc, f.info, warnings))
 }
 
diff --git a/crates/engine/src/lib.rs b/crates/engine/src/lib.rs
index b7c789ab..0157f169 100644
--- a/crates/engine/src/lib.rs
+++ b/crates/engine/src/lib.rs
@@ -583,6 +583,10 @@ pub(crate) fn is_guide_path(d: &Document, id: NodeId) -> bool {
     d.node(id).is_some_and(|n| matches!(n.kind, NodeKind::Path { guide: true, .. }))
 }
 
+/// The error of an edit that would nest objects deeper than [`vectorcraft_doc::MAX_DEPTH`].
+pub const TOO_DEEP: &str = "objects can't be nested more than 32 deep";
+const _: () = assert!(vectorcraft_doc::MAX_DEPTH == 32, "TOO_DEEP (and its catalog rows) names the cap");
+
 /// Cheap sanity check after an edit: artboards and the objects just touched (the selection) must
 /// have finite, in-range geometry, so saved files always reload and renderers never see NaN/∞.
 fn doc_sane(d: &Document, sel: &Selection) -> bool {
@@ -1245,6 +1249,9 @@ impl Session {
     }
     /// Add a document and make it active.
     pub fn add_document(&mut self, mut doc: Document, path: Option<String>) -> usize {
+        // Every edit is checked against the document before it, so the first one is within the cap
+        // (importers and the native reader have seen to theirs already, with a warning).
+        doc.limit_depth();
         Self::refresh_text_bounds(&mut doc);
         // Guides from files saved before guides had layers go on a layer.
         doc.adopt_guides();
@@ -1262,6 +1269,7 @@ impl Session {
         if index >= self.docs.len() {
             return false;
         }
+        doc.limit_depth();
         Self::refresh_text_bounds(&mut doc);
         doc.adopt_guides();
         if self.active == Some(index) {
@@ -1476,7 +1484,10 @@ impl Session {
                     if !st.doc.variables.bindings.is_empty() {
                         Arc::make_mut(&mut st.doc).prune_variable_bindings();
                     }
-                    if doc_sane(&st.doc, &st.selection) {
+                    if st.doc.too_deep(Some(&before)) {
+                        // Deeper trees overflow the stack of what walks them.
+                        Err(EngineError::Other(TOO_DEEP.into()))
+                    } else if doc_sane(&st.doc, &st.selection) {
                         Ok(v)
                     } else {
                         Err(EngineError::Other("result would exceed the canvas (coordinates out of range)".into()))
diff --git a/crates/engine/tests/import_fuzz.rs b/crates/engine/tests/import_fuzz.rs
index 7d7c9d62..84a9cc85 100644
--- a/crates/engine/tests/import_fuzz.rs
+++ b/crates/engine/tests/import_fuzz.rs
@@ -2440,3 +2440,345 @@ proptest! {
         checked("mutated script", json!({"dataBase64": vectorcraft_format::base64_encode(&bytes), "name": "sample.jsx"}))?;
     }
 }
+
+// ---------- deep nesting ----------
+//
+// The tree is walked by recursion, so a file nested deeply enough overflowed the stack: an abort,
+// which nothing catches. Every reader caps what it reads, and no document is deeper than
+// `MAX_DEPTH`. These run on a thread with the stack of a Windows main thread (1 MB), where an
+// overflow ends the test run.
+
+use vectorcraft_doc::MAX_DEPTH;
+
+/// `f` on a thread with a 1 MB stack.
+fn on_a_small_stack(f: impl FnOnce() + Send + 'static) {
+    std::thread::Builder::new().stack_size(1 << 20).spawn(f).unwrap().join().unwrap();
+}
+
+/// Open `bytes` as the file `name`: an error, or a document within the cap that renders and
+/// exports. Returns the document and the import's warnings.
+fn open_deep(name: &str, bytes: &[u8]) -> Option<(Document, Vec<String>)> {
+    let loaded = vectorcraft_engine::cmd::fileio::load(name, bytes).ok()?;
+    assert!(!loaded.doc.too_deep(None), "{name}: deeper than the cap");
+    let doc = loaded.doc.clone();
+    survive(name, move || Some(doc)).unwrap();
+    Some((loaded.doc, loaded.warnings))
+}
+
+fn merged(warnings: &[String]) -> bool {
+    warnings.iter().any(|w| w.contains("nested more than"))
+}
+
+fn paths_in(doc: &Document) -> usize {
+    let mut paths = 0;
+    doc.walk(|n| paths += usize::from(n.path_data().is_some()));
+    paths
+}
+
+const SVG_NS: &str = "xmlns=\"http://www.w3.org/2000/svg\"";
+
+/// `n` groups in one another, each named (so it is kept) and with a rectangle beside the next.
+fn nested_svg(n: usize) -> String {
+    let open: String = (0..n).map(|i| format!("<g id=\"g{i}\"><rect width=\"5\" height=\"5\"/>")).collect();
+    format!("<svg {SVG_NS} width=\"100\" height=\"100\">{open}<rect width=\"10\" height=\"10\"/>{}</svg>", "</g>".repeat(n))
+}
+
+#[test]
+fn deeply_nested_svg_is_refused_or_merged() {
+    on_a_small_stack(|| {
+        // Within what the reader takes: opened, the groups past the cap merged into the last.
+        let (doc, warnings) = open_deep("deep.svg", nested_svg(40).as_bytes()).expect("40 groups open");
+        assert!(merged(&warnings), "{warnings:?}");
+        assert_eq!(paths_in(&doc), 41, "no art is lost");
+        let (_, warnings) = open_deep("shallow.svg", nested_svg(20).as_bytes()).expect("20 groups open");
+        assert!(!merged(&warnings), "{warnings:?}");
+        // As deep as the reader goes (on a stack of its own): opened and merged the same.
+        let most = vectorcraft_svg::MAX_ELEMENT_DEPTH;
+        let (doc, warnings) = open_deep("deepest.svg", nested_svg(most - 2).as_bytes()).expect("opens at the reader's cap");
+        assert!(merged(&warnings), "{warnings:?}");
+        assert_eq!(paths_in(&doc), most - 1, "no art is lost");
+        // Past it: an error that says why, whatever the depth.
+        for n in [most, 2 * most, 200_000] {
+            let e = vectorcraft_engine::cmd::fileio::load("deep.svg", nested_svg(n).as_bytes()).err().expect("refused").to_string();
+            assert!(e.contains(&format!("nested more than {most} deep")), "{n}: {e}");
+        }
+        // Unnamed groups of one object aren't kept, but usvg walks them all the same.
+        let plain = format!(
+            "<svg {SVG_NS} width=\"9\" height=\"9\">{}<rect width=\"1\" height=\"1\"/>{}</svg>",
+            "<g>".repeat(2 * most),
+            "</g>".repeat(2 * most)
+        );
+        assert!(open_deep("plain.svg", plain.as_bytes()).is_none());
+        // A chain of `<use>`: shallow XML, a deep tree.
+        let links: String = (0..3000).map(|i| format!("<g id=\"u{i}\"><use href=\"#u{}\"/></g>", i + 1)).collect();
+        let chain = format!(
+            "<svg {SVG_NS} width=\"9\" height=\"9\"><defs>{links}<rect id=\"u3000\" width=\"1\" height=\"1\"/></defs><use href=\"#u0\"/></svg>"
+        );
+        assert!(open_deep("chain.svg", chain.as_bytes()).is_none());
+        // Placed and pasted, as opened.
+        let mut s = vectorcraft_engine::Session::new();
+        s.execute("file.new", &json!({"width": 300, "height": 200})).unwrap();
+        for n in [40, 2 * most] {
+            let p = json!({"name": "deep.svg", "dataBase64": vectorcraft_format::base64_encode(nested_svg(n).as_bytes())});
+            let _ = no_panic(s.execute("file.place", &p));
+            let _ = no_panic(s.execute("clipboard.importSvg", &json!({"svg": nested_svg(n)})));
+            let _ = no_panic(s.execute("edit.paste", &json!({})));
+            assert!(!s.doc().unwrap().doc.too_deep(None));
+        }
+    });
+}
+
+/// A page whose content is `content`, with `resources`.
+fn deep_pdf(content: &str, resources: &str) -> Vec<u8> {
+    handmade_pdf(content, resources, "[0 0 100 100]")
+}
+
+/// An EPS whose program is `body`.
+fn deep_eps(body: &str) -> Vec<u8> {
+    format!("%!PS-Adobe-3.0 EPSF-3.0\n%%BoundingBox: 0 0 100 100\n%%EndComments\n{body}\nshowpage\n%%EOF\n").into_bytes()
+}
+
+/// A test for each file: it opens as an error or as a document within the cap, on a small stack.
+macro_rules! deep_files {
+    ($($test:ident: $name:literal, $bytes:expr;)*) => {$(
+        #[test]
+        fn $test() {
+            on_a_small_stack(|| {
+                open_deep($name, &$bytes);
+            });
+        }
+    )*};
+}
+
+deep_files! {
+    // PDF: clips inside clips (saved states never restored); arrays in arrays as an operand and as
+    // an object; dictionaries in dictionaries as a resource and inline; marked content never ended.
+    pdf_clips_in_clips: "clips.pdf", deep_pdf(&format!("{} 0 0 5 5 re f", "q 0 0 50 50 re W n ".repeat(20_000)), "<< >>");
+    pdf_arrays_in_an_operand: "arrays.pdf", deep_pdf(&format!("BT {}{} TJ ET 0 0 5 5 re f", "[".repeat(100_000), "]".repeat(100_000)), "<< >>");
+    pdf_arrays_in_an_object: "boxes.pdf", handmade_pdf("0 0 5 5 re f", "<< >>", &format!("{}0 0 100 100{}", "[".repeat(100_000), "]".repeat(100_000)));
+    pdf_dictionaries_in_resources: "dicts.pdf", deep_pdf("0 0 5 5 re f", &format!("{}{}", "<< /A ".repeat(50_000), ">> ".repeat(50_000)));
+    pdf_dictionaries_in_content: "inline.pdf", deep_pdf(&format!("/P {}{} DP 0 0 5 5 re f", "<< /A ".repeat(50_000), ">> ".repeat(50_000)), "<< >>");
+    pdf_marked_content_never_ended: "marked.pdf", deep_pdf(&format!("{} 0 0 5 5 re f", "/Span << /MCID 0 >> BDC ".repeat(50_000)), "<< >>");
+    // PostScript: clips inside clips; procedures in procedures; arrays in arrays; a procedure that
+    // calls itself; dictionaries never ended.
+    eps_clips_in_clips: "clips.eps", deep_eps(&format!("{} 0 0 5 5 rectfill", "gsave 0 0 50 50 rectclip ".repeat(20_000)));
+    eps_procedures_in_procedures: "procs.eps", deep_eps(&format!("{}{} 0 0 5 5 rectfill", "{".repeat(100_000), "}".repeat(100_000)));
+    eps_arrays_in_arrays: "arrays.eps", deep_eps(&format!("{}{} pop 0 0 5 5 rectfill", "[".repeat(100_000), "]".repeat(100_000)));
+    eps_a_procedure_calling_itself: "runaway.eps", deep_eps("/f { 0 0 5 5 rectfill f } def f");
+    eps_dictionaries_never_ended: "dicts.eps", deep_eps(&format!("{} 0 0 5 5 rectfill", "1 dict begin ".repeat(100_000)));
+}
+
+#[test]
+fn deeply_nested_dxf_blocks_are_read_within_the_cap() {
+    on_a_small_stack(|| {
+        // Block `B0` inserts `B1`, which inserts `B2`, and so on; the last one holds a line.
+        let pair = |c: i32, v: &str| (c, v.to_string());
+        let mut pairs = vec![pair(0, "SECTION"), pair(2, "BLOCKS")];
+        for i in 0..2_000 {
+            pairs.extend([pair(0, "BLOCK"), pair(2, &format!("B{i}")), pair(10, "0"), pair(20, "0")]);
+            if i + 1 < 2_000 {
+                pairs.extend([pair(0, "INSERT"), pair(2, &format!("B{}", i + 1)), pair(10, "1"), pair(20, "1")]);
+            } else {
+                pairs.extend([pair(0, "LINE"), pair(10, "0"), pair(20, "0"), pair(11, "5"), pair(21, "5")]);
+            }
+            pairs.push(pair(0, "ENDBLK"));
+        }
+        pairs.extend([pair(0, "ENDSEC"), pair(0, "SECTION"), pair(2, "ENTITIES"), pair(0, "INSERT"), pair(2, "B0"), pair(10, "0"), pair(20, "0")]);
+        pairs.extend([pair(0, "LINE"), pair(10, "0"), pair(20, "0"), pair(11, "9"), pair(21, "9"), pair(0, "ENDSEC"), pair(0, "EOF")]);
+        open_deep("blocks.dxf", dxf_text(&pairs).as_bytes()).expect("opens");
+    });
+}
+
+/// A layer holding `levels` groups in one another around a rectangle, each with a second
+/// rectangle beside the next: `levels + 2` deep.
+fn nested_document(levels: usize) -> Document {
+    use vectorcraft_doc::Node;
+    use vectorcraft_testkit::fixtures::DocBuilder;
+    let mut b = DocBuilder::new(100.0, 100.0);
+    let rect =
+        |b: &mut DocBuilder, x: f64| b.rect_node(vectorcraft_geom::Rect::new(x, 0.0, x + 10.0, 10.0), vectorcraft_color::Color::rgb8(200, 0, 0));
+    let mut inner = rect(&mut b, 0.0);
+    for _ in 0..levels {
+        let beside = rect(&mut b, 20.0);
+        inner = Node::group(b.alloc(), vec![std::sync::Arc::new(inner), std::sync::Arc::new(beside)]);
+        inner.opacity = 0.9;
+    }
+    b.add(inner);
+    b.build()
+}
+
+#[test]
+fn a_document_at_the_cap_saves_opens_and_exports() {
+    on_a_small_stack(|| {
+        let doc = nested_document(MAX_DEPTH - 2);
+        assert!(!doc.too_deep(None));
+        let back = vectorcraft_format::load_file(&vectorcraft_format::save_file(&doc)).expect("what can be made opens again");
+        assert!(back.depth_notes.is_empty());
+        assert_eq!(back.doc.layers, doc.layers);
+        survive("at the cap", || Some(doc.clone())).unwrap();
+        // Every format that keeps the nesting reads its own file back within the cap.
+        let mut s = vectorcraft_engine::Session::new();
+        s.add_document(doc, None);
+        for format in ["svg", "pdf", "eps", "ai"] {
+            let r = s.execute("document.export", &json!({"format": format})).unwrap();
+            let bytes = vectorcraft_format::base64_decode(r["dataBase64"].as_str().unwrap()).unwrap();
+            open_deep(&format!("cap.{format}"), &bytes).unwrap_or_else(|| panic!("{format} opens"));
+        }
+        for cmd in ["select.all", "document.inspect", "document.info", "edit.copy", "edit.paste", "object.ungroup", "edit.undo"] {
+            no_panic(s.execute(cmd, &json!({}))).unwrap_or_else(|e| panic!("{cmd}: {e}"));
+        }
+    });
+}
+
+#[test]
+fn a_native_file_nested_too_deep_is_merged_or_refused() {
+    on_a_small_stack(|| {
+        // Saved before the cap by a version that could still open it: opened, the deepest merged.
+        let old = vectorcraft_format::save_file(&nested_document(MAX_DEPTH + 2));
+        let (doc, warnings) = open_deep("old.vectorcraft", &old).expect("opens");
+        assert!(merged(&warnings), "{warnings:?}");
+        assert_eq!(paths_in(&doc), MAX_DEPTH + 3, "no art is lost");
+        // Deeper than any version could open, and a hostile file: an error that says why. Written
+        // by hand: a tree this deep can't be built and saved.
+        let text = String::from_utf8(vectorcraft_format::save(&nested_document(0), false)).unwrap();
+        let (open, close) = ("{\"id\":900000,\"kind\":{\"type\":\"group\",\"children\":[", "]}}");
+        let at = text.find("\"children\":[").expect("the layer's children") + "\"children\":[".len();
+        for levels in [100, 50_000] {
+            let deep = format!("{}{}{},{}", &text[..at], open.repeat(levels), close.repeat(levels), &text[at..]);
+            let e = vectorcraft_engine::cmd::fileio::load("deep.vectorcraft", deep.as_bytes()).err().expect("refused").to_string();
+            assert!(e.contains("nested too deep"), "{levels}: {e}");
+        }
+    });
+}
+
+#[test]
+fn commands_cannot_nest_deeper_than_the_cap() {
+    on_a_small_stack(|| {
+        let mut s = vectorcraft_engine::Session::new();
+        s.execute("file.new", &json!({"width": 200, "height": 200})).unwrap();
+        s.execute("shape.rectangle", &json!({"x": 10, "y": 10, "width": 50, "height": 50})).unwrap();
+        s.execute("select.all", &json!({})).unwrap();
+        let mut grouped = 0;
+        for _ in 0..10_000 {
+            match no_panic(s.execute("object.group", &json!({}))) {
+                Ok(_) => grouped += 1,
+                Err(e) => assert!(e.to_string().contains(vectorcraft_engine::TOO_DEEP), "after {grouped} groups: {e}"),
+            }
+        }
+        // The layer, the groups and the rectangle.
+        assert_eq!(grouped, MAX_DEPTH - 2);
+        assert!(!s.doc().unwrap().doc.too_deep(None));
+        // Other ways down: a clipping mask, a copy pasted, a symbol made of it.
+        for (cmd, p) in [
+            ("object.clippingMask.make", json!({})),
+            ("edit.copy", json!({})),
+            ("edit.pasteInFront", json!({})),
+            ("symbol.new", json!({"name": "deep"})),
+        ] {
+            let _ = no_panic(s.execute(cmd, &p));
+            assert!(!s.doc().unwrap().doc.too_deep(None), "{cmd}");
+        }
+        survive("grouped to the cap", || Some((*s.doc().unwrap().doc).clone())).unwrap();
+    });
+}
+
+/// A document whose one object is an instance of the first of `count` symbols: each symbol's art
+/// is `levels` groups around an instance of the next symbol, the last one of `last`.
+fn symbols_document(count: usize, levels: usize, last: &str) -> Document {
+    use vectorcraft_doc::{Node, NodeKind, Symbol};
+    let instance =
+        |doc: &mut Document, of: String| Node::new(doc.alloc_id(), NodeKind::SymbolInstance { symbol: of, xf: vectorcraft_geom::Affine::IDENTITY });
+    let mut doc = nested_document(1);
+    for i in 0..count {
+        let mut art = instance(&mut doc, if i + 1 < count { format!("s{}", i + 1) } else { last.to_string() });
+        for _ in 0..levels {
+            art = Node::group(doc.alloc_id(), vec![std::sync::Arc::new(art)]);
+        }
+        doc.symbols.push(Symbol { name: format!("s{i}"), art: std::sync::Arc::new(art) });
+    }
+    let first = instance(&mut doc, "s0".into());
+    let layer = doc.layers[0].id;
+    doc.insert(Some(layer), usize::MAX, first).unwrap();
+    doc
+}
+
+/// `doc` saved (as an older version, or a hostile file, could have) and opened again: within the
+/// caps (`kept`: as it was), drawn, exported and edited.
+fn symbols_survive(what: &str, doc: Document, kept: bool) {
+    let (back, warnings) = open_deep("symbols.vectorcraft", &vectorcraft_format::save_file(&doc)).expect("opens");
+    assert_eq!(!warnings.iter().any(|w| w.contains("symbol instances")), kept, "{what}: {warnings:?}");
+    let mut s = vectorcraft_engine::Session::new();
+    s.add_document(back, None);
+    for cmd in [
+        "select.all",
+        "document.inspect",
+        "document.info",
+        "object.expand",
+        "symbol.breakLink",
+        "object.flattenTransparency",
+        "edit.copy",
+        "edit.paste",
+    ] {
+        let _ = no_panic(s.execute(cmd, &json!({})));
+        assert!(!s.doc().unwrap().doc.too_deep(None), "{what}: {cmd}");
+    }
+    for format in ["svg", "pdf", "eps", "png"] {
+        let _ = no_panic(s.execute("document.export", &json!({"format": format})));
+    }
+}
+
+#[test]
+fn a_symbol_holding_itself_opens_without_the_instance() {
+    on_a_small_stack(|| {
+        symbols_survive("a symbol holding itself", symbols_document(1, 1, "s0"), false);
+        symbols_survive("symbols holding one another", symbols_document(3, 2, "s0"), false);
+    });
+}
+
+#[test]
+fn symbols_in_symbols_are_drawn_only_so_deep() {
+    on_a_small_stack(|| {
+        // As deep as symbols draw: each one's art as deep as art goes.
+        symbols_survive("symbols at the cap", symbols_document(3, MAX_DEPTH - 2, "none"), true);
+        symbols_survive("symbols in symbols", symbols_document(40, MAX_DEPTH - 1, "none"), false);
+        // A symbol can't be made to hold itself, or one that holds it, by editing either.
+        let mut s = vectorcraft_engine::Session::new();
+        s.add_document(symbols_document(2, 1, "none"), None);
+        s.execute("select.all", &json!({})).unwrap();
+        for (cmd, p) in [
+            ("symbol.new", json!({"name": "s1"})),
+            ("symbol.update", json!({"name": "s1"})),
+            ("symbol.update", json!({"name": "s0"})),
+            ("symbol.replace", json!({"name": "s1"})),
+        ] {
+            let _ = no_panic(s.execute(cmd, &p));
+            assert!(!s.doc().unwrap().doc.too_deep(None), "{cmd} {p}");
+        }
+    });
+}
+
+#[test]
+fn a_pattern_painting_its_own_tile_opens_without_the_paint() {
+    on_a_small_stack(|| {
+        use vectorcraft_color::Paint;
+        use vectorcraft_doc::{Appearance, PatternDef};
+        let painted = |doc: &mut Document, with: &str| {
+            let fill = Paint::Pattern { pattern: with.into(), xf: vectorcraft_geom::Affine::IDENTITY };
+            let square = vectorcraft_geom::shapes::rectangle(vectorcraft_geom::Rect::new(0.0, 0.0, 20.0, 20.0));
+            vectorcraft_doc::Node::path(doc.alloc_id(), square, Appearance::basic(fill, Paint::None, 0.0))
+        };
+        // One pattern painting its own tile, and two painting each other's.
+        for names in [["p", "p"], ["p", "q"]] {
+            let mut doc = nested_document(1);
+            let (first, second) = (painted(&mut doc, names[1]), painted(&mut doc, names[0]));
+            doc.patterns.push(PatternDef::new(names[0], vec![std::sync::Arc::new(first)]));
+            if names[0] != names[1] {
+                doc.patterns.push(PatternDef::new(names[1], vec![std::sync::Arc::new(second)]));
+            }
+            let on_layer = painted(&mut doc, "p");
+            let layer = doc.layers[0].id;
+            doc.insert(Some(layer), usize::MAX, on_layer).unwrap();
+            symbols_survive("a pattern painting its own tile", doc, false);
+        }
+    });
+}
diff --git a/crates/eps/src/import/interp.rs b/crates/eps/src/import/interp.rs
index 6104d1b5..f74b5df0 100644
--- a/crates/eps/src/import/interp.rs
+++ b/crates/eps/src/import/interp.rs
@@ -4,7 +4,6 @@
 //! Every operation counts against a budget and procedures nest only so deep, so a looping or
 //! recursing program ends with [`PsError::Limit`] instead of hanging.
 
-use std::cell::RefCell;
 use std::rc::Rc;
 
 use vectorcraft_geom::Affine;
@@ -86,7 +85,7 @@ struct SaveMark {
 }
 
 fn new_dict() -> DictRef {
-    Rc::new(RefCell::new(Dict::new()))
+    DictRef::new(Dict::new())
 }
 
 /// An encoding vector: 256 `/.notdef` names (type is read as Latin-1 whatever the encoding).
diff --git a/crates/eps/src/import/mod.rs b/crates/eps/src/import/mod.rs
index 3be867a7..276cc981 100644
--- a/crates/eps/src/import/mod.rs
+++ b/crates/eps/src/import/mod.rs
@@ -268,5 +268,7 @@ fn finish_with(out: Out, layers: Vec<Arc<Node>>) -> Imported {
         }
     }
     doc.layers = layers;
-    Imported { document: doc, warnings: out.warnings, preview: false }
+    let mut warnings = out.warnings;
+    doc.limit_depth_noting(&mut warnings);
+    Imported { document: doc, warnings, preview: false }
 }
diff --git a/crates/eps/src/import/native.rs b/crates/eps/src/import/native.rs
index a4355a76..7a979de4 100644
--- a/crates/eps/src/import/native.rs
+++ b/crates/eps/src/import/native.rs
@@ -993,6 +993,7 @@ fn build(data: &[u8], visible: Option<&Document>, page: Page, outlined: bool, tr
         }
         None => unmark(&mut doc.layers, true, &mut vec![]),
     }
+    doc.limit_depth_noting(&mut notes);
     Ok((doc, notes))
 }
 
diff --git a/crates/eps/src/import/obj.rs b/crates/eps/src/import/obj.rs
index 220f79dc..ae8f7a8e 100644
--- a/crates/eps/src/import/obj.rs
+++ b/crates/eps/src/import/obj.rs
@@ -12,7 +12,73 @@ use super::graphics::GState;
 pub(crate) type Dict = HashMap<Key, Obj>;
 
 /// A shared, mutable dictionary.
-pub(crate) type DictRef = Rc<RefCell<Dict>>;
+#[derive(Clone, Debug)]
+pub(crate) struct DictRef(Rc<RefCell<Dict>>);
+
+impl DictRef {
+    pub fn new(d: Dict) -> Self {
+        Self(Rc::new(RefCell::new(d)))
+    }
+}
+
+impl std::ops::Deref for DictRef {
+    type Target = Rc<RefCell<Dict>>;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl Drop for DictRef {
+    fn drop(&mut self) {
+        if Rc::strong_count(&self.0) == 1
+            && let Ok(mut d) = self.0.try_borrow_mut()
+        {
+            drop_held(d.drain().map(|(_, v)| v));
+        }
+    }
+}
+
+thread_local! {
+    /// What the composite objects being dropped held, waiting for their turn (while any is).
+    static HELD: RefCell<Option<Vec<Obj>>> = const { RefCell::new(None) };
+}
+
+/// Drop what a composite object held, now that nothing else refers to it, without recursion: a
+/// program nests arrays and dictionaries as deep as it likes (`[ exch ]` in a loop), and dropping
+/// them one inside the other overflows the stack. What `held` holds in its turn waits in [`HELD`]
+/// for the outermost drop, which works through it.
+fn drop_held(held: impl Iterator<Item = Obj>) {
+    let holds = |o: &Obj| matches!(o, Obj::Array { .. } | Obj::Dict(_) | Obj::File { .. } | Obj::GState(_));
+    // (Without the list, when the thread is ending: dropped as they come.)
+    let outermost = HELD.try_with(|h| {
+        let Ok(mut h) = h.try_borrow_mut() else { return false };
+        let outermost = h.is_none();
+        h.get_or_insert_with(Vec::new).extend(held.filter(holds));
+        outermost
+    });
+    if !matches!(outermost, Ok(true)) {
+        return;
+    }
+    // Each drop here puts what it held on the list instead of dropping it.
+    while let Ok(Some(next)) = HELD.try_with(|h| h.try_borrow_mut().ok().and_then(|mut h| h.as_mut().and_then(Vec::pop))) {
+        drop(next);
+    }
+    let _ = HELD.try_with(|h| h.try_borrow_mut().map(|mut h| *h = None)); // Nothing to do when the thread is ending.
+}
+
+/// What [`Shared`] values may be: bytes, or objects (which may hold more of themselves).
+pub(crate) trait Held: Sized {
+    /// Drop the values of storage nothing refers to any more.
+    fn release(_values: Vec<Self>) {}
+}
+
+impl Held for u8 {}
+
+impl Held for Obj {
+    fn release(values: Vec<Self>) {
+        drop_held(values.into_iter());
+    }
+}
 
 /// A dictionary key.
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
@@ -72,7 +138,7 @@ impl Obj {
     }
 
     pub fn dict(d: Dict) -> Self {
-        Self::Dict(Rc::new(RefCell::new(d)))
+        Self::Dict(DictRef::new(d))
     }
 
     /// The number this is (integers and reals).
@@ -135,13 +201,23 @@ impl Obj {
 /// The values of a string or an array: a run of storage that other strings or arrays may share
 /// (`getinterval` makes a new object over part of the same values, as PostScript does).
 #[derive(Clone, Debug)]
-pub(crate) struct Shared<T> {
+pub(crate) struct Shared<T: Held> {
     buf: Rc<RefCell<Vec<T>>>,
     at: usize,
     len: usize,
 }
 
-impl<T: Clone> Shared<T> {
+impl<T: Held> Drop for Shared<T> {
+    fn drop(&mut self) {
+        if Rc::strong_count(&self.buf) == 1
+            && let Ok(mut values) = self.buf.try_borrow_mut()
+        {
+            T::release(std::mem::take(&mut *values));
+        }
+    }
+}
+
+impl<T: Clone + Held> Shared<T> {
     pub fn new(v: Vec<T>) -> Self {
         Self { len: v.len(), buf: Rc::new(RefCell::new(v)), at: 0 }
     }
@@ -198,7 +274,7 @@ impl<T: Clone> Shared<T> {
 }
 
 /// Hashes what [`Shared::same`] compares: the storage and the run of it.
-impl<T> Hash for Shared<T> {
+impl<T: Held> Hash for Shared<T> {
     fn hash<H: Hasher>(&self, state: &mut H) {
         Rc::as_ptr(&self.buf).hash(state);
         (self.at, self.len).hash(state);
diff --git a/crates/eps/src/import/text.rs b/crates/eps/src/import/text.rs
index 9c8cd673..248f011b 100644
--- a/crates/eps/src/import/text.rs
+++ b/crates/eps/src/import/text.rs
@@ -389,7 +389,7 @@ impl Interp<'_> {
         d.insert(Key::name("FontMatrix"), matrix_obj(Affine::scale(0.001)));
         d.insert(Key::name("FontBBox"), Obj::array(vec![Obj::Int(0), Obj::Int(-250), Obj::Int(1000), Obj::Int(1000)]));
         d.insert(Key::name("Encoding"), Obj::array(vec![Obj::name(".notdef"); 256]));
-        let font = Rc::new(std::cell::RefCell::new(d));
+        let font = DictRef::new(d);
         self.fonts.borrow_mut().insert(key, Obj::Dict(font.clone()));
         Ok(font)
     }
@@ -489,7 +489,7 @@ fn transformed(font: &DictRef, m: Affine) -> DictRef {
     let mut d = font.borrow().clone();
     let fm = d.get(&Key::name("FontMatrix")).and_then(|o| o.items().and_then(|i| matrix_of(&i.borrow()))).unwrap_or(Affine::scale(0.001));
     d.insert(Key::name("FontMatrix"), matrix_obj(m * fm));
-    Rc::new(std::cell::RefCell::new(d))
+    DictRef::new(d)
 }
 
 /// The character a glyph name stands for (`A`, `space`, `uni20AC`), else a bullet.
diff --git a/crates/format/src/lib.rs b/crates/format/src/lib.rs
index e6891e1e..4811b8ca 100644
--- a/crates/format/src/lib.rs
+++ b/crates/format/src/lib.rs
@@ -482,6 +482,9 @@ pub fn load(bytes: &[u8]) -> Result<Document, FormatError> {
 #[derive(Debug)]
 pub struct NativeFile {
     pub doc: Document,
+    /// What was done to bring the document within the nesting caps
+    /// ([`Document::limit_depth_noting`]: a file saved before them, or a damaged one).
+    pub depth_notes: Vec<String>,
     pub info: FileInfo,
     /// ICC files by profile name (saved with Embed ICC Profiles; undecodable ones are left out).
     pub profiles: BTreeMap<String, Vec<u8>>,
@@ -511,7 +514,11 @@ pub fn load_info(bytes: &[u8]) -> Result<(Document, FileInfo), FormatError> {
 /// [`load`], with everything else the file carries.
 pub fn load_file(bytes: &[u8]) -> Result<NativeFile, FormatError> {
     let file = unpack::Unpacked::new(bytes)?;
-    let f: File = serde_json::from_slice(file.json()).map_err(|e| FormatError::NotVectorcraft(e.to_string()))?;
+    // The JSON reader stops at 128 levels (a document's objects use three each).
+    let f: File = serde_json::from_slice(file.json()).map_err(|e| {
+        let why = if e.to_string().contains("recursion limit") { format!("its objects are nested too deep ({e})") } else { e.to_string() };
+        FormatError::NotVectorcraft(why)
+    })?;
     if f.format != EXTENSION && f.format != LEGACY_EXTENSION {
         return Err(FormatError::NotVectorcraft(format!("format is `{}`", f.format)));
     }
@@ -545,8 +552,10 @@ pub fn load_file(bytes: &[u8]) -> Result<NativeFile, FormatError> {
     // Untrusted: capped, named and pointing at objects the file has.
     doc.tidy_saved_selections();
     doc.tidy_graph_designs();
+    let mut depth_notes = vec![];
+    doc.limit_depth_noting(&mut depth_notes);
     let profiles = f.profiles.into_iter().filter_map(|(name, icc)| Some((name, bytes_of(&icc)?))).collect();
-    Ok(NativeFile { doc, info: FileInfo { version: f.version, legacy: f.format == LEGACY_EXTENSION }, profiles })
+    Ok(NativeFile { doc, depth_notes, info: FileInfo { version: f.version, legacy: f.format == LEGACY_EXTENSION }, profiles })
 }
 
 /// The members of a native file besides its document (which is skipped, not decoded).
diff --git a/crates/metafile/src/lib.rs b/crates/metafile/src/lib.rs
index b1ab24fc..f51c2c8e 100644
--- a/crates/metafile/src/lib.rs
+++ b/crates/metafile/src/lib.rs
@@ -102,7 +102,9 @@ pub struct Imported {
 /// Read an EMF or WMF file (with or without a placeable header) into a document whose one
 /// artboard is the picture's frame.
 pub fn import(bytes: &[u8]) -> Result<Imported, String> {
-    import::import(bytes)
+    let mut i = import::import(bytes)?;
+    i.document.limit_depth_noting(&mut i.warnings);
+    Ok(i)
 }
 
 #[cfg(test)]
diff --git a/crates/pdf/src/import.rs b/crates/pdf/src/import.rs
index 1c4ca1b3..d3116ce6 100644
--- a/crates/pdf/src/import.rs
+++ b/crates/pdf/src/import.rs
@@ -149,6 +149,7 @@ pub const PAST_PAGE_NOTE: &str = "art reaching past the page was clipped to it,
 pub fn import_with_report(bytes: &[u8], opts: &ImportOptions) -> Result<ImportReport, PdfError> {
     let original = crate::pages::open(bytes, opts.password.as_deref())?;
     let picked = crate::pages::picked(opts, original.pages().len())?;
+    picked.iter().filter_map(|&n| original.pages().get(n)).try_for_each(crate::pages::content_too_deep)?;
     let mut ocgs = Ocgs::read(&original);
     let route = opts.layers && !ocgs.list.is_empty();
     // Content that is off imports as hidden layers: an update of the file turns every group on
@@ -166,6 +167,7 @@ pub fn import_with_report(bytes: &[u8], opts: &ImportOptions) -> Result<ImportRe
     let all_on = turned_on.is_some();
     let pdf = turned_on.unwrap_or(original);
     let pages = pdf.pages();
+    picked.iter().filter_map(|&n| pages.get(n)).try_for_each(crate::pages::content_too_deep)?;
 
     let sink: Arc<Mutex<Vec<String>>> = Arc::default();
     let sink2 = sink.clone();
@@ -417,6 +419,7 @@ pub fn import_with_report(bytes: &[u8], opts: &ImportOptions) -> Result<ImportRe
             }
         }
     }
+    doc.limit_depth_noting(&mut warnings);
     Ok(ImportReport { document: doc, warnings, native: crate::editing::editing_in(&pdf), only_text })
 }
 
diff --git a/crates/pdf/src/pages.rs b/crates/pdf/src/pages.rs
index 5a98c40c..29817514 100644
--- a/crates/pdf/src/pages.rs
+++ b/crates/pdf/src/pages.rs
@@ -33,12 +33,76 @@ pub fn is_postscript(bytes: &[u8]) -> bool {
     bytes.starts_with(b"%!PS") || bytes.starts_with(&[0xC5, 0xD0, 0xD3, 0xC6])
 }
 
+/// The deepest a file's arrays and dictionaries may nest. The PDF reader (hayro) reads them by
+/// recursion, without a cap of its own: a file nested deeply enough overflows the stack, which is
+/// an abort, not an error. Far beyond what a PDF writer makes.
+const MAX_OBJECT_NESTING: usize = 256;
+
+fn too_deep() -> PdfError {
+    PdfError::Parse(format!("its arrays and dictionaries are nested more than {MAX_OBJECT_NESTING} deep"))
+}
+
+/// Do the arrays and dictionaries in the text of `pdf` nest deeper than [`MAX_OBJECT_NESTING`]?
+/// Read as tokens (strings and comments hold none), an object at a time. The data of a stream
+/// with a filter is skipped: it isn't PDF text until decoded, which this doesn't do, so nesting
+/// inside compressed streams is not seen here.
+fn nests_too_deep(pdf: &[u8]) -> bool {
+    let after =
+        |from: usize, what: &[u8]| pdf.get(from..).and_then(|rest| rest.windows(what.len()).position(|w| w == what)).map(|at| from + at + what.len());
+    let word = |at: usize, w: &[u8]| pdf.get(at..).is_some_and(|rest| rest.starts_with(w));
+    let (mut depth, mut filtered) = (0usize, false);
+    let mut i = 0;
+    while let Some(&c) = pdf.get(i) {
+        i += 1;
+        match c {
+            b'%' => i += pdf.get(i..).and_then(|rest| rest.iter().position(|c| matches!(c, b'\n' | b'\r'))).unwrap_or(pdf.len()),
+            b'(' => {
+                // A string: parentheses nest in it, a backslash takes the next byte.
+                let mut open = 1usize;
+                while open > 0 {
+                    match pdf.get(i) {
+                        None => return false,
+                        Some(b'\\') => i += 1,
+                        Some(b'(') => open += 1,
+                        Some(b')') => open -= 1,
+                        Some(_) => {}
+                    }
+                    i += 1;
+                }
+            }
+            b'[' => depth += 1,
+            b']' => depth = depth.saturating_sub(1),
+            b'<' if pdf.get(i) == Some(&b'<') => (depth, i) = (depth + 1, i + 1),
+            b'>' if pdf.get(i) == Some(&b'>') => (depth, i) = (depth.saturating_sub(1), i + 1),
+            // A string in hexadecimal.
+            b'<' => i = after(i, b">").unwrap_or(pdf.len()),
+            b'/' if word(i - 1, b"/Filter") => filtered = true,
+            b'e' if word(i - 1, b"endobj") => (depth, filtered) = (0, false),
+            b'e' if word(i - 1, b"endstream") => i += 8,
+            b's' if word(i - 1, b"stream") => {
+                depth = 0;
+                if std::mem::take(&mut filtered) {
+                    i = after(i, b"endstream").unwrap_or(pdf.len());
+                }
+            }
+            _ => {}
+        }
+        if depth > MAX_OBJECT_NESTING {
+            return true;
+        }
+    }
+    false
+}
+
 /// Read a PDF, decrypting it with `password` (none: the empty user password). The permissions
 /// password opens a file too.
 pub(crate) fn open(bytes: &[u8], password: Option<&str>) -> Result<Pdf, PdfError> {
     if is_postscript(bytes) {
         return Err(PdfError::PostScript);
     }
+    if nests_too_deep(bytes) {
+        return Err(too_deep());
+    }
     let password = password.unwrap_or_default();
     let read = |pw: &str| Pdf::new_with_password(bytes.to_vec(), pw);
     read(password)
@@ -57,6 +121,12 @@ pub(crate) fn open(bytes: &[u8], password: Option<&str>) -> Result<Pdf, PdfError
         })
 }
 
+/// The error of a page whose content, decoded, nests arrays and dictionaries too deep (see
+/// [`MAX_OBJECT_NESTING`]): its operands are read the same way as the file's objects.
+pub(crate) fn content_too_deep(page: &Page<'_>) -> Result<(), PdfError> {
+    if page.page_stream().is_some_and(nests_too_deep) { Err(too_deep()) } else { Ok(()) }
+}
+
 /// The pages and their boxes. An encrypted PDF needs its `password`
 /// ([`PdfError::NeedsPassword`] / [`PdfError::WrongPassword`]).
 pub fn info(bytes: &[u8], password: Option<&str>) -> Result<PdfInfo, PdfError> {
diff --git a/crates/svg/src/import.rs b/crates/svg/src/import.rs
index 323621e1..dc65646e 100644
--- a/crates/svg/src/import.rs
+++ b/crates/svg/src/import.rs
@@ -18,10 +18,13 @@ use crate::{ImportOptions, SvgError, fnv1a};
 use css::XNode;
 use text::TextSlots;
 
+pub use depth::MAX_ELEMENT_DEPTH;
+pub(crate) use depth::xml_too_deep;
 pub(crate) use fx::BLEND;
 
 mod css;
 mod css_transform;
+mod depth;
 mod files;
 mod fx;
 mod spread;
@@ -29,11 +32,30 @@ mod symbol_units;
 mod text;
 mod vector_effect;
 
+/// The XML of `svg`.
+fn parse(svg: &str) -> Result<roxmltree::Document<'_>, SvgError> {
+    roxmltree::Document::parse_with_options(svg, roxmltree::ParsingOptions { allow_dtd: true, ..Default::default() })
+        .map_err(|e| SvgError::Parse(e.to_string()))
+}
+
 pub(crate) fn import(svg: &str, opts: &ImportOptions) -> Result<(Document, Vec<String>), SvgError> {
-    let (svg, found) = prepass(svg, opts);
+    // Before anything reads the tree: the XML reader, usvg, and what is made of its tree, all by
+    // recursion.
+    let too_deep = || SvgError::TooDeep(depth::MAX_ELEMENT_DEPTH);
+    if depth::xml_too_deep(svg) {
+        return Err(too_deep());
+    }
+    let xml = parse(svg)?;
+    if depth::too_deep(&xml) {
+        return Err(too_deep());
+    }
+    let (svg, found) = prepass(svg, &xml, opts);
+    // The prepass's edits are in the text: the XML is read again only when it made any.
+    let xml = match &svg {
+        Cow::Borrowed(_) => xml,
+        Cow::Owned(edited) => parse(edited)?,
+    };
     let svg = svg.as_ref();
-    let xml = roxmltree::Document::parse_with_options(svg, roxmltree::ParsingOptions { allow_dtd: true, ..Default::default() })
-        .map_err(|e| SvgError::Parse(e.to_string()))?;
     let units = RootUnits::of(xml.root_element());
     let root_name = root_layer_name(xml.root_element());
     let mut warnings = found.warnings;
@@ -165,6 +187,7 @@ pub(crate) fn import(svg: &str, opts: &ImportOptions) -> Result<(Document, Vec<S
             promote_sublayers(Arc::make_mut(l), &im.sublayer_groups);
         }
     }
+    im.doc.limit_depth_noting(&mut im.warnings);
     Ok((im.doc, im.warnings))
 }
 
@@ -554,7 +577,7 @@ impl Edits {
 /// * linked files are read ([`files`]);
 /// * percentage lengths in a `<symbol>` with a `viewBox` become numbers ([`symbol_units`]);
 /// * what style sheet rules with a `:not()` set goes in `style` attributes ([`not_rules`]).
-fn prepass<'s>(svg: &'s str, opts: &ImportOptions) -> (Cow<'s, str>, Found) {
+fn prepass<'s>(svg: &'s str, xml: &roxmltree::Document, opts: &ImportOptions) -> (Cow<'s, str>, Found) {
     let mut found = Found::default();
     // (`:` for prefixed elements such as `<svg:image>`.)
     let css_transform = has_css_transform(svg);
@@ -565,9 +588,6 @@ fn prepass<'s>(svg: &'s str, opts: &ImportOptions) -> (Cow<'s, str>, Found) {
     {
         return (svg.into(), found);
     }
-    let Ok(xml) = roxmltree::Document::parse_with_options(svg, roxmltree::ParsingOptions { allow_dtd: true, ..Default::default() }) else {
-        return (svg.into(), found);
-    };
     let mut edits = Edits::default();
     let elements = || xml.descendants().filter(|n| n.is_element());
     for a in elements().filter(|n| n.tag_name().name() == "a") {
@@ -592,24 +612,24 @@ fn prepass<'s>(svg: &'s str, opts: &ImportOptions) -> (Cow<'s, str>, Found) {
     }
     let (display, non_scaling) = (svg.contains("display"), svg.contains(vector_effect::NON_SCALING));
     if display || non_scaling || not {
-        let css = css::Styles::new(&xml);
+        let css = css::Styles::new(xml);
         // First: an undisplayed object shown for usvg is shown after these.
         if not && css.has_not_rules() {
-            not_rules(svg, &xml, &css, &mut edits);
+            not_rules(svg, xml, &css, &mut edits);
         }
         if display {
-            hidden_objects(svg, &xml, &css, &mut edits, &mut found.hidden);
+            hidden_objects(svg, xml, &css, &mut edits, &mut found.hidden);
         }
         if non_scaling {
-            vector_effect::find(svg, &xml, &css, &mut edits, &mut found.non_scaling, &mut found.warnings);
+            vector_effect::find(svg, xml, &css, &mut edits, &mut found.non_scaling, &mut found.warnings);
         }
     }
-    found.files = files::Files::read(svg, &xml, opts, &mut edits, &mut found.warnings);
+    found.files = files::Files::read(svg, xml, opts, &mut edits, &mut found.warnings);
     if !symbols.is_empty() && svg.contains('%') {
-        edits.list.extend(symbol_units::rewrites(&xml));
+        edits.list.extend(symbol_units::rewrites(xml));
     }
     if css_transform {
-        edits.list.extend(css_transform::rewrites(svg, &xml));
+        edits.list.extend(css_transform::rewrites(svg, xml));
     }
     (edits.apply(svg), found)
 }
diff --git a/crates/svg/src/import/css.rs b/crates/svg/src/import/css.rs
index 8f508a7f..86eb6767 100644
--- a/crates/svg/src/import/css.rs
+++ b/crates/svg/src/import/css.rs
@@ -17,7 +17,7 @@ pub(super) type XNode<'a, 'i> = roxmltree::Node<'a, 'i>;
 
 /// `name: value` declarations of a block or `style` attribute, with their `!important` flag. The
 /// `font` shorthand becomes its longhands, as usvg reads it for the rest of the drawing (#1557).
-fn parse_decls(s: &str) -> Vec<(String, String, bool)> {
+pub(super) fn parse_decls(s: &str) -> Vec<(String, String, bool)> {
     s.split(';')
         .filter_map(|d| {
             let (k, v) = d.split_once(':')?;
@@ -371,8 +371,13 @@ impl Styles {
         Self { rules, index, cache: RefCell::default() }
     }
 
+    /// Do the document's style sheets have any rules?
+    pub(super) fn has_rules(&self) -> bool {
+        !self.rules.is_empty()
+    }
+
     /// Properties set on `n` by rules and its `style` attribute, after the cascade.
-    fn declared(&self, n: XNode) -> Rc<HashMap<String, String>> {
+    pub(super) fn declared(&self, n: XNode) -> Rc<HashMap<String, String>> {
         if let Some(m) = self.cache.borrow().get(&n.id()) {
             return m.clone();
         }
diff --git a/crates/svg/src/import/depth.rs b/crates/svg/src/import/depth.rs
new file mode 100644
index 00000000..3febdd96
--- /dev/null
+++ b/crates/svg/src/import/depth.rs
@@ -0,0 +1,264 @@
+//! How deep an SVG's elements nest, found in the XML before usvg runs: usvg converts the tree by
+//! recursion, a few stack frames an element, so a file nested deeply enough overflows the stack
+//! (an abort, not an error). Such a file is refused: its nesting can't be merged before usvg has
+//! read it, and usvg is what can't read it.
+//!
+//! What counts is the tree usvg walks, not the XML alone: a `<use>` holds a copy of what it
+//! refers to, and a clip path, mask, pattern, marker or filter is converted where it is used
+//! (`clip-path: url(#a)` on an element of a clip path makes a chain as deep as there are clip
+//! paths). So each element's depth is the deepest of what it holds and what it refers to.
+
+use std::collections::HashMap;
+use std::collections::hash_map::Entry;
+
+use usvg::roxmltree;
+
+use super::css::{Styles, XNode, parse_decls};
+
+/// The deepest an SVG's elements may nest, references followed. Far beyond what drawing apps
+/// write, and deeper than a document's objects may nest ([`vectorcraft_doc::MAX_DEPTH`]: wrappers
+/// that hold one object aren't kept, and what is still deeper is merged into the group around
+/// it). usvg uses about 15 kB of stack for each level: the importer runs on a thread with 16 MB
+/// ([`vectorcraft_doc::depth::with_deep_stack`]), except on the web, where there is the one
+/// 1 MB stack.
+pub const MAX_ELEMENT_DEPTH: usize = if cfg!(target_arch = "wasm32") { 48 } else { 256 };
+
+/// Properties whose value an element's descendants use too: the paint server they name is
+/// converted at each descendant, under everything between.
+const INHERITED: [&str; 6] = ["fill", "stroke", "marker", "marker-start", "marker-mid", "marker-end"];
+
+/// The ids of the `url(#id)` references in a property value.
+fn urls(value: &str) -> impl Iterator<Item = &str> {
+    value.split("url(").skip(1).filter_map(|rest| {
+        let id = rest.trim_start().trim_start_matches(['"', '\'']).strip_prefix('#')?;
+        id.split([')', '"', '\'']).next().map(str::trim).filter(|id| !id.is_empty())
+    })
+}
+
+/// The elements `n` refers to, each with whether `n`'s descendants use it too.
+fn references<'a, 'i>(n: XNode<'a, 'i>, ids: &HashMap<&str, XNode<'a, 'i>>, css: &Styles, out: &mut Vec<(XNode<'a, 'i>, bool)>) {
+    let add = |out: &mut Vec<(XNode<'a, 'i>, bool)>, name: &str, value: &str| {
+        let inherited = INHERITED.contains(&name);
+        out.extend(urls(value).filter_map(|id| ids.get(id)).map(|t| (*t, inherited)));
+    };
+    for a in n.attributes() {
+        match a.name() {
+            "href" => out.extend(a.value().trim().strip_prefix('#').and_then(|id| ids.get(id)).map(|t| (*t, false))),
+            // Read with the style sheets' rules below.
+            "style" if css.has_rules() => {}
+            "style" => parse_decls(a.value()).iter().for_each(|(k, v, _)| add(out, k, v)),
+            name => add(out, name, a.value()),
+        }
+    }
+    if css.has_rules() {
+        css.declared(n).iter().for_each(|(k, v)| add(out, k, v));
+    }
+}
+
+/// Do the elements of the XML text `svg` nest deeper than [`MAX_ELEMENT_DEPTH`]? Read from the
+/// text, before any XML reader: roxmltree (ours and usvg's) reads elements by recursion too. Tags
+/// are counted as the text has them; markup in the values of a document type's entities counts
+/// ten times (how deep entities may refer to one another), on top of the deepest element.
+pub(crate) fn xml_too_deep(svg: &str) -> bool {
+    let b = svg.as_bytes();
+    let find =
+        |from: usize, what: &[u8]| b.get(from..).and_then(|rest| rest.windows(what.len()).position(|w| w == what)).map(|at| from + at + what.len());
+    // The end of the tag starting at `from` (past its `>`), and whether it closes itself.
+    let tag_end = |from: usize| {
+        let mut quote = None;
+        for (i, c) in b.iter().enumerate().skip(from) {
+            match (quote, c) {
+                (None, b'"' | b'\'') => quote = Some(*c),
+                (Some(q), c) if q == *c => quote = None,
+                (None, b'>') => return (i + 1, b.get(i.wrapping_sub(1)) == Some(&b'/')),
+                _ => {}
+            }
+        }
+        (b.len(), false)
+    };
+    // (now, deepest) of the elements, and of the markup inside the document type.
+    let (mut elements, mut entities) = ((0usize, 0usize), (0usize, 0usize));
+    let mut doctype_end = 0;
+    let mut i = 0;
+    while let Some(at) = b.get(i..).and_then(|rest| rest.iter().position(|c| *c == b'<')).map(|at| i + at) {
+        let rest = b.get(at..).unwrap_or_default();
+        let depth = if at < doctype_end { &mut entities } else { &mut elements };
+        i = if rest.starts_with(b"<!--") {
+            find(at, b"-->").unwrap_or(b.len())
+        } else if rest.starts_with(b"<![CDATA[") {
+            find(at, b"]]>").unwrap_or(b.len())
+        } else if rest.starts_with(b"<?") {
+            find(at, b"?>").unwrap_or(b.len())
+        } else if rest.starts_with(b"<!DOCTYPE") {
+            // Up to the `>` that ends it: after its internal subset (`[` … `]`) when it has one.
+            let plain = tag_end(at).0;
+            let subset = b.get(at..plain).is_some_and(|head| head.contains(&b'['));
+            doctype_end = if subset { find(at, b"]>").unwrap_or(b.len()) } else { plain };
+            at + 2
+        } else if rest.starts_with(b"<!") {
+            // A declaration of the document type: the markup in its value is counted as it comes.
+            at + 2
+        } else if rest.starts_with(b"</") {
+            depth.0 = depth.0.saturating_sub(1);
+            tag_end(at).0
+        } else if at < doctype_end {
+            // In an entity's value, itself in quotes: up to the tag's `>`.
+            let end = find(at, b">").unwrap_or(b.len());
+            depth.1 = depth.1.max(depth.0 + 1);
+            depth.0 += usize::from(b.get(end.wrapping_sub(2)) != Some(&b'/'));
+            end
+        } else {
+            let (end, empty) = tag_end(at);
+            depth.1 = depth.1.max(depth.0 + 1);
+            depth.0 += usize::from(!empty);
+            end
+        };
+        if elements.1 + 10 * entities.1 > MAX_ELEMENT_DEPTH {
+            return true;
+        }
+    }
+    false
+}
+
+/// Does anything in `xml` nest deeper than [`MAX_ELEMENT_DEPTH`], references followed? Without
+/// recursion.
+pub(super) fn too_deep(xml: &roxmltree::Document) -> bool {
+    let elements = || xml.descendants().filter(|n| n.is_element());
+    let ids: HashMap<&str, XNode> = elements().filter_map(|n| Some((n.attribute("id")?, n))).collect();
+    let css = Styles::new(xml);
+    // How deep each element's own tree goes, itself included; 0 while it is being worked out: a
+    // reference back to it then is a loop, which usvg leaves out.
+    let mut heights: HashMap<roxmltree::NodeId, usize> = HashMap::new();
+    enum Step<'a, 'i> {
+        Enter(XNode<'a, 'i>),
+        Leave(XNode<'a, 'i>, Vec<(XNode<'a, 'i>, bool)>),
+    }
+    let mut stack = vec![Step::Enter(xml.root_element())];
+    while let Some(step) = stack.pop() {
+        match step {
+            Step::Enter(n) => {
+                match heights.entry(n.id()) {
+                    Entry::Occupied(_) => continue,
+                    Entry::Vacant(v) => v.insert(0),
+                };
+                let mut refs = vec![];
+                references(n, &ids, &css, &mut refs);
+                let targets: Vec<XNode> = refs.iter().map(|(t, _)| *t).collect();
+                stack.push(Step::Leave(n, refs));
+                stack.extend(n.children().filter(|c| c.is_element()).chain(targets).map(Step::Enter));
+            }
+            Step::Leave(n, refs) => {
+                let of = |n: XNode| heights.get(&n.id()).copied().unwrap_or(0);
+                let held = n.children().filter(|c| c.is_element()).map(of).max().unwrap_or(0);
+                let used = |inherited: bool| refs.iter().filter(|(_, i)| *i == inherited).map(|(t, _)| of(*t)).max().unwrap_or(0);
+                let height = 1 + held.max(used(false)) + used(true);
+                if height > MAX_ELEMENT_DEPTH {
+                    return true;
+                }
+                heights.insert(n.id(), height);
+            }
+        }
+    }
+    false
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn deep(svg: &str) -> bool {
+        too_deep(&roxmltree::Document::parse(svg).unwrap())
+    }
+
+    fn svg(body: &str) -> String {
+        format!(r#"<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="10" height="10">{body}</svg>"#)
+    }
+
+    /// `n` groups in one another around a rectangle.
+    fn groups(n: usize) -> String {
+        format!("{}<rect width='1' height='1'/>{}", "<g>".repeat(n), "</g>".repeat(n))
+    }
+
+    #[test]
+    fn elements_nest_up_to_the_cap() {
+        // The root, the groups and the rectangle.
+        let (at, past) = (svg(&groups(MAX_ELEMENT_DEPTH - 2)), svg(&groups(MAX_ELEMENT_DEPTH - 1)));
+        assert!(!deep(&at) && !xml_too_deep(&at));
+        assert!(deep(&past) && xml_too_deep(&past));
+        assert!(xml_too_deep(&svg(&groups(200_000))), "any depth is measured");
+    }
+
+    #[test]
+    fn the_text_is_measured_as_xml_reads_it() {
+        let many = r#"<g a='>' b="<g>"><rect/></g>"#.repeat(500);
+        assert!(!xml_too_deep(&svg(&many)), "side by side, with `>` and tags in attribute values");
+        let hidden = format!("<!-- {0} --><![CDATA[{0}]]><?pi {0}?>", "<g>".repeat(500));
+        assert!(!xml_too_deep(&svg(&hidden)), "comments, character data and instructions hold no elements");
+        assert!(xml_too_deep(&format!("<svg>{}", "<g>".repeat(MAX_ELEMENT_DEPTH))), "never closed");
+        assert!(!xml_too_deep(&format!("{}<svg/>", "</g>".repeat(2 * MAX_ELEMENT_DEPTH))), "ends without beginnings");
+        // Entities: namespaces as drawing apps declare them, and markup that would be read ten deep.
+        let names = r#"<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd" [ <!ENTITY ns_svg "http://www.w3.org/2000/svg"> ]>"#;
+        assert!(!xml_too_deep(&format!("{names}{}", svg(&groups(30)))));
+        let tenth = MAX_ELEMENT_DEPTH / 10 + 1;
+        let bomb = format!("<!DOCTYPE svg [ <!ENTITY a \"{}&a;{}\"> ]>", "<g>".repeat(tenth), "</g>".repeat(tenth));
+        assert!(xml_too_deep(&format!("{bomb}<svg>&a;</svg>")));
+        assert!(!xml_too_deep(""));
+    }
+
+    #[test]
+    fn a_chain_of_uses_is_as_deep_as_what_it_copies() {
+        let chain = |n: usize| {
+            let defs: String = (0..n).map(|i| format!("<g id='g{i}'><use xlink:href='#g{}'/></g>", i + 1)).collect();
+            svg(&format!("<defs>{defs}<rect id='g{n}' width='1' height='1'/></defs><use href='#g0'/>"))
+        };
+        assert!(!deep(&chain(10)));
+        assert!(deep(&chain(MAX_ELEMENT_DEPTH / 2)), "two elements a link");
+        assert!(deep(&chain(5000)));
+    }
+
+    #[test]
+    fn chains_of_clips_masks_and_patterns_count_by_attribute_style_and_style_sheet() {
+        let by_attribute = |n: usize| -> String {
+            (0..n).map(|i| format!("<clipPath id='c{i}' clip-path='url(#c{})'><rect width='1' height='1'/></clipPath>", i + 1)).collect()
+        };
+        let by_style = |n: usize| -> String {
+            (0..n).map(|i| format!("<mask id='c{i}' style='mask: url( \"#c{}\" )'><rect width='1' height='1'/></mask>", i + 1)).collect()
+        };
+        let by_sheet = |n: usize| -> String {
+            let rules: String = (0..n).map(|i| format!(".p{i} {{ fill: url(#c{}) }}", i + 1)).collect();
+            let patterns: String = (0..n)
+                .map(|i| format!("<pattern id='c{i}' width='1' height='1'><g class='p{i}'><rect width='1' height='1'/></g></pattern>"))
+                .collect();
+            format!("<style>{rules}</style>{patterns}")
+        };
+        for chain in [&by_attribute as &dyn Fn(usize) -> String, &by_style, &by_sheet] {
+            let file =
+                |n| svg(&format!("<defs>{}</defs><rect width='5' height='5' fill='url(#c0)' clip-path='url(#c0)' mask='url(#c0)'/>", chain(n)));
+            assert!(!deep(&file(5)));
+            assert!(deep(&file(MAX_ELEMENT_DEPTH)));
+        }
+    }
+
+    #[test]
+    fn many_paint_servers_used_side_by_side_are_not_a_chain() {
+        // As drawing apps write gradients: a class each, used by objects that aren't inside one another.
+        let rules: String = (0..300).map(|i| format!(".c{i}{{fill:url(#g{i})}}")).collect();
+        let defs: String = (0..300).map(|i| format!("<linearGradient id='g{i}'><stop class='c{i}' offset='0'/></linearGradient>")).collect();
+        let art: String = (0..300).map(|i| format!("<g class='c{i}'><rect class='c{i}' width='1' height='1'/></g>")).collect();
+        assert!(!deep(&svg(&format!("<style>{rules}</style><defs>{defs}</defs>{art}"))));
+    }
+
+    #[test]
+    fn a_loop_of_references_is_not_deep() {
+        assert!(!deep(&svg("<g id='a'><use href='#b'/></g><g id='b'><use href='#a'/></g><clipPath id='c' clip-path='url(#c)'/>")));
+    }
+
+    #[test]
+    fn an_inherited_paint_is_converted_under_everything_between() {
+        // Neither the pattern nor the art is too deep; the pattern under the art's last object is.
+        let half = MAX_ELEMENT_DEPTH / 2;
+        let pattern = format!("<pattern id='p' width='1' height='1'>{}</pattern>", groups(half));
+        assert!(!deep(&svg(&format!("<defs>{pattern}</defs><g fill='url(#p)'>{}</g>", groups(half / 2)))));
+        assert!(deep(&svg(&format!("<defs>{pattern}</defs><g fill='url(#p)'>{}</g>", groups(half)))));
+    }
+}
diff --git a/crates/svg/src/import/files.rs b/crates/svg/src/import/files.rs
index bbe33d84..88607277 100644
--- a/crates/svg/src/import/files.rs
+++ b/crates/svg/src/import/files.rs
@@ -203,12 +203,16 @@ impl Files {
         ImageHrefResolver {
             resolve_data: Box::new(move |mime, bytes, opts| {
                 if mime == "image/svg+xml" {
+                    if nested_too_deep(&bytes) {
+                        return None;
+                    }
                     self.note_text(&bytes);
                 }
                 data(mime, bytes, opts)
             }),
             resolve_string: Box::new(move |h, opts| match self.sources.get(h).or_else(|| self.sources.get(h.trim()))? {
                 Source::Raster(kind, bytes) => Some(kind(bytes.clone())),
+                Source::Svg(bytes) if nested_too_deep(bytes) => None,
                 Source::Svg(bytes) => {
                     self.note_text(bytes);
                     usvg::Tree::from_data_nested(bytes, opts).ok().map(ImageKind::SVG)
@@ -218,6 +222,12 @@ impl Files {
     }
 }
 
+/// Is the SVG image `bytes` nested too deep for usvg to read (as the SVG holding it would be)?
+/// It is then left out, as an image usvg can't read.
+fn nested_too_deep(bytes: &[u8]) -> bool {
+    crate::text_of(bytes).is_ok_and(|text| super::xml_too_deep(&text))
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/crates/svg/src/lib.rs b/crates/svg/src/lib.rs
index 7cbc8531..2f1f3c5e 100644
--- a/crates/svg/src/lib.rs
+++ b/crates/svg/src/lib.rs
@@ -312,6 +312,9 @@ pub struct LinkedImage {
 pub enum SvgError {
     #[error("SVG parse error: {0}")]
     Parse(String),
+    /// Its elements nest (references followed) deeper than the reader goes.
+    #[error("the SVG's elements are nested more than {0} deep")]
+    TooDeep(usize),
 }
 
 /// Export a document as an SVG string (linked images are not returned: see [`export_full`]).
@@ -347,7 +350,8 @@ pub struct Editing {
 
 /// The native document an SVG carries, if any, and whether the SVG was edited since.
 pub fn editing(svg: &str) -> Option<Editing> {
-    if !svg.contains(EDITING_NS) {
+    // (An SVG nested too deep for the XML reader carries none: it isn't one of ours.)
+    if !svg.contains(EDITING_NS) || import::xml_too_deep(svg) {
         return None;
     }
     let opts = usvg::roxmltree::ParsingOptions { allow_dtd: true, ..Default::default() };
@@ -500,14 +504,18 @@ pub fn import_with_report(svg: &str) -> Result<(Document, Vec<String>), SvgError
     import_with(svg, &ImportOptions::default())
 }
 
+pub use import::MAX_ELEMENT_DEPTH;
+
 /// Import an SVG document reading the files it links to as `opts` says, also returning warnings.
 pub fn import_with(svg: &str, opts: &ImportOptions) -> Result<(Document, Vec<String>), SvgError> {
-    import::import(svg, opts)
+    // usvg converts the tree by recursion, in large stack frames: the nesting it is given is
+    // capped (`import::depth`), and it gets room for that cap whatever thread asks.
+    vectorcraft_doc::depth::with_deep_stack(|| import::import(svg, opts))
 }
 
 /// Reads a linked file: its bytes and the link to it (absolute path, size, time and hash), or
 /// `None` when there is no readable file at the (absolute) path.
-pub type ReadFile<'a> = &'a dyn Fn(&str) -> Option<(Vec<u8>, vectorcraft_doc::LinkInfo)>;
+pub type ReadFile<'a> = &'a (dyn Fn(&str) -> Option<(Vec<u8>, vectorcraft_doc::LinkInfo)> + Sync);
 
 /// How [`import_with`] reads the files an SVG's `<image>` elements link to.
 ///
diff --git a/crates/ui-egui/src/i18n/cs.tsv b/crates/ui-egui/src/i18n/cs.tsv
index 9a58680f..522b6fce 100644
--- a/crates/ui-egui/src/i18n/cs.tsv
+++ b/crates/ui-egui/src/i18n/cs.tsv
@@ -4099,6 +4099,8 @@ imageTrace	Outline	Obrys
 @msg	recovery copy `{file}`: {e}	kopie pro obnovení `{file}`: {e}
 @msg	resolutions must be between 1 and 2400 ppi	rozlišení musí být mezi 1 a 2400 ppi
 @msg	result would exceed the canvas (coordinates out of range)	výsledek by přesáhl plátno (souřadnice mimo rozsah)
+@msg	objects can't be nested more than 32 deep	objekty nelze vnořit hlouběji než do 32 úrovní
+@msg	the SVG's elements are nested more than {0} deep	prvky SVG jsou vnořeny hlouběji než do {0} úrovní
 @msg	scale must be a number from {_1} to {_2}, not {_3}	měřítko musí být číslo od {_1} do {_2}, ne {_3}
 @msg	scale must be a number from {_1} to {_2}, not {s}	měřítko musí být číslo od {_1} do {_2}, ne {s}
 @msg	select (or target) objects whose appearance isn't basic	vyberte (nebo zacilte) objekty, jejichž vzhled není základní
diff --git a/crates/ui-egui/src/i18n/de.tsv b/crates/ui-egui/src/i18n/de.tsv
index 24af8f75..bda4f451 100644
--- a/crates/ui-egui/src/i18n/de.tsv
+++ b/crates/ui-egui/src/i18n/de.tsv
@@ -3705,6 +3705,8 @@ theme	Appearance	Erscheinungsbild
 @msg	recovery copy `{file}`: {e}	Wiederherstellungskopie `{file}`: {e}
 @msg	resolutions must be between 1 and 2400 ppi	Auflösungen müssen zwischen 1 und 2400 ppi liegen
 @msg	result would exceed the canvas (coordinates out of range)	das Ergebnis würde die Arbeitsfläche überschreiten (Koordinaten außerhalb des Bereichs)
+@msg	objects can't be nested more than 32 deep	Objekte können nicht tiefer als 32 Ebenen verschachtelt werden
+@msg	the SVG's elements are nested more than {0} deep	die Elemente der SVG-Datei sind tiefer als {0} Ebenen verschachtelt
 @msg	scale must be a number from {_1} to {_2}, not {_3}	scale muss eine Zahl von {_1} bis {_2} sein, nicht {_3}
 @msg	scale must be a number from {_1} to {_2}, not {s}	scale muss eine Zahl von {_1} bis {_2} sein, nicht {s}
 @msg	select (or target) objects whose appearance isn't basic	wählen Sie Objekte aus (oder als Ziel), deren Aussehen nicht einfach ist
diff --git a/crates/ui-egui/src/i18n/es.tsv b/crates/ui-egui/src/i18n/es.tsv
index 91c49142..c9c36d04 100644
--- a/crates/ui-egui/src/i18n/es.tsv
+++ b/crates/ui-egui/src/i18n/es.tsv
@@ -3804,6 +3804,8 @@ axis	Both	Ambos
 @msg	recovery copy `{file}`: {e}	copia de recuperación `{file}`: {e}
 @msg	resolutions must be between 1 and 2400 ppi	las resoluciones deben estar entre 1 y 2400 ppi
 @msg	result would exceed the canvas (coordinates out of range)	el resultado excedería el lienzo (coordenadas fuera de rango)
+@msg	objects can't be nested more than 32 deep	los objetos no pueden anidarse a más de 32 niveles
+@msg	the SVG's elements are nested more than {0} deep	los elementos del SVG están anidados a más de {0} niveles
 @msg	scale must be a number from {_1} to {_2}, not {_3}	la escala debe ser un número de {_1} a {_2}, no {_3}
 @msg	scale must be a number from {_1} to {_2}, not {s}	la escala debe ser un número de {_1} a {_2}, no {s}
 @msg	select (or target) objects whose appearance isn't basic	selecciona (o apunta a) objetos cuya apariencia no sea básica
diff --git a/crates/ui-egui/src/i18n/fr.tsv b/crates/ui-egui/src/i18n/fr.tsv
index 3226266a..de2b62f6 100644
--- a/crates/ui-egui/src/i18n/fr.tsv
+++ b/crates/ui-egui/src/i18n/fr.tsv
@@ -3801,6 +3801,8 @@ axis	Both	Les deux
 @msg	recovery copy `{file}`: {e}	copie de récupération `{file}` : {e}
 @msg	resolutions must be between 1 and 2400 ppi	les résolutions doivent être comprises entre 1 et 2400 ppp
 @msg	result would exceed the canvas (coordinates out of range)	le résultat dépasserait la zone de travail (coordonnées hors limites)
+@msg	objects can't be nested more than 32 deep	les objets ne peuvent pas être imbriqués sur plus de 32 niveaux
+@msg	the SVG's elements are nested more than {0} deep	les éléments du SVG sont imbriqués sur plus de {0} niveaux
 @msg	scale must be a number from {_1} to {_2}, not {_3}	l’échelle doit être un nombre compris entre {_1} et {_2}, pas {_3}
 @msg	scale must be a number from {_1} to {_2}, not {s}	l’échelle doit être un nombre compris entre {_1} et {_2}, pas {s}
 @msg	select (or target) objects whose appearance isn't basic	sélectionnez (ou ciblez) des objets dont l’aspect n’est pas basique
diff --git a/crates/ui-egui/src/i18n/hu.tsv b/crates/ui-egui/src/i18n/hu.tsv
index 961caaa0..488b5a9f 100644
--- a/crates/ui-egui/src/i18n/hu.tsv
+++ b/crates/ui-egui/src/i18n/hu.tsv
@@ -4441,6 +4441,8 @@ imageTrace	Outline	Körvonal
 @msg	resolutions must be between 1 and 2400 ppi	a felbontás 1 és 2400 ppi között lehet
 @msg	Restored {_1} recovered document(s): save them to keep them	Helyreállított dokumentumok: {_1}; mentsd őket, ha meg akarod tartani
 @msg	result would exceed the canvas (coordinates out of range)	az eredmény túllépné a vásznat (a koordináták tartományon kívül esnek)
+@msg	objects can't be nested more than 32 deep	az objektumok legfeljebb 32 szint mélyen ágyazhatók egymásba
+@msg	the SVG's elements are nested more than {0} deep	az SVG elemei több mint {0} szint mélyen vannak egymásba ágyazva
 @msg	Save for Web: the image is empty	Mentés webre: a kép üres
 @msg	Save writes {_1}, not {_2}: use document.export for other formats	a Mentés ezt írja: {_1}, ezt nem: {_2}; más formátumhoz használd a document.export parancsot
 @msg	saved panel layout is invalid; reset the workspace first	a mentett panelelrendezés érvénytelen; előbb állítsd vissza a munkaterületet
diff --git a/crates/ui-egui/src/i18n/it.tsv b/crates/ui-egui/src/i18n/it.tsv
index 3353c5bc..1facacf4 100644
--- a/crates/ui-egui/src/i18n/it.tsv
+++ b/crates/ui-egui/src/i18n/it.tsv
@@ -3804,6 +3804,8 @@ axis	Both	Entrambi
 @msg	recovery copy `{file}`: {e}	copia di recupero `{file}`: {e}
 @msg	resolutions must be between 1 and 2400 ppi	le risoluzioni devono essere comprese tra 1 e 2400 ppi
 @msg	result would exceed the canvas (coordinates out of range)	il risultato supererebbe l'area di disegno (coordinate fuori intervallo)
+@msg	objects can't be nested more than 32 deep	gli oggetti non possono essere nidificati oltre 32 livelli
+@msg	the SVG's elements are nested more than {0} deep	gli elementi dell'SVG sono nidificati oltre {0} livelli
 @msg	scale must be a number from {_1} to {_2}, not {_3}	la scala deve essere un numero da {_1} a {_2}, non {_3}
 @msg	scale must be a number from {_1} to {_2}, not {s}	la scala deve essere un numero da {_1} a {_2}, non {s}
 @msg	select (or target) objects whose appearance isn't basic	seleziona (o imposta come destinazione) oggetti con un aspetto non di base
diff --git a/crates/ui-egui/src/i18n/ja.tsv b/crates/ui-egui/src/i18n/ja.tsv
index b2361baf..8eef3ae6 100644
--- a/crates/ui-egui/src/i18n/ja.tsv
+++ b/crates/ui-egui/src/i18n/ja.tsv
@@ -3730,6 +3730,8 @@ theme	Appearance	外観
 @msg	no interaction in progress	進行中の操作がありません
 @msg	no such object {0}	オブジェクト {0} が見つかりません
 @msg	result would exceed the canvas (coordinates out of range)	結果がカンバスの範囲を超えます (座標が範囲外です)
+@msg	objects can't be nested more than 32 deep	オブジェクトは 32 階層より深く入れ子にできません
+@msg	the SVG's elements are nested more than {0} deep	SVG の要素が {0} 階層より深く入れ子になっています
 @msg	unknown command `{0}`	`{0}` は不明なコマンドです
 @msg	`{what}` closes nothing	`{what}` に対応する開始部分がありません
 @msg	`{what}` closes something it didn't open	`{what}` が対応しない開始部分を閉じています
diff --git a/crates/ui-egui/src/i18n/ko.tsv b/crates/ui-egui/src/i18n/ko.tsv
index d964a99e..2b944e13 100644
--- a/crates/ui-egui/src/i18n/ko.tsv
+++ b/crates/ui-egui/src/i18n/ko.tsv
@@ -3708,6 +3708,8 @@ theme	Appearance	외관
 @msg	no interaction in progress	진행 중인 상호작용이 없습니다
 @msg	no such object {0}	개체 {0}이(가) 없습니다
 @msg	result would exceed the canvas (coordinates out of range)	결과가 캔버스를 벗어납니다(좌표 범위 초과)
+@msg	objects can't be nested more than 32 deep	개체는 32단계보다 깊게 중첩할 수 없습니다
+@msg	the SVG's elements are nested more than {0} deep	SVG 요소가 {0}단계보다 깊게 중첩되어 있습니다
 @msg	unknown command `{0}`	알 수 없는 명령 `{0}`
 @msg	`{what}` closes nothing	`{what}`이(가) 닫는 항목이 없습니다
 @msg	`{what}` closes something it didn't open	`{what}`이(가) 열지 않은 항목을 닫습니다
diff --git a/crates/ui-egui/src/i18n/pl.tsv b/crates/ui-egui/src/i18n/pl.tsv
index 5a8df065..4c26ef01 100644
--- a/crates/ui-egui/src/i18n/pl.tsv
+++ b/crates/ui-egui/src/i18n/pl.tsv
@@ -3965,6 +3965,8 @@ imageTrace	Outline	Kontur
 @msg	recovery copy `{file}`: {e}	kopia odzyskiwania `{file}`: {e}
 @msg	resolutions must be between 1 and 2400 ppi	rozdzielczości muszą mieścić się w zakresie od 1 do 2400 ppi
 @msg	result would exceed the canvas (coordinates out of range)	wynik wykroczyłby poza płótno (współrzędne poza zakresem)
+@msg	objects can't be nested more than 32 deep	obiektów nie można zagnieżdżać głębiej niż na 32 poziomy
+@msg	the SVG's elements are nested more than {0} deep	elementy SVG są zagnieżdżone głębiej niż na {0} poziomów
 @msg	scale must be a number from {_1} to {_2}, not {_3}	skala musi być liczbą od {_1} do {_2}, nie {_3}
 @msg	scale must be a number from {_1} to {_2}, not {s}	skala musi być liczbą od {_1} do {_2}, nie {s}
 @msg	select (or target) objects whose appearance isn't basic	zaznacz (lub wskaż) obiekty, których wygląd nie jest podstawowy
diff --git a/crates/ui-egui/src/i18n/pt-br.tsv b/crates/ui-egui/src/i18n/pt-br.tsv
index 75a81dca..a5c87a70 100644
--- a/crates/ui-egui/src/i18n/pt-br.tsv
+++ b/crates/ui-egui/src/i18n/pt-br.tsv
@@ -3449,6 +3449,8 @@ axis	Both	Ambos
 @msg	recovery copy `{file}`: {e}	cópia de recuperação `{file}`: {e}
 @msg	resolutions must be between 1 and 2400 ppi	as resoluções devem estar entre 1 e 2400 ppi
 @msg	result would exceed the canvas (coordinates out of range)	o resultado excederia a tela (coordenadas fora do intervalo)
+@msg	objects can't be nested more than 32 deep	os objetos não podem ser aninhados em mais de 32 níveis
+@msg	the SVG's elements are nested more than {0} deep	os elementos do SVG estão aninhados em mais de {0} níveis
 @msg	scale must be a number from {_1} to {_2}, not {_3}	a escala deve ser um número de {_1} a {_2}, não {_3}
 @msg	scale must be a number from {_1} to {_2}, not {s}	a escala deve ser um número de {_1} a {_2}, não {s}
 @msg	select (or target) objects whose appearance isn't basic	selecione (ou direcione) objetos cuja aparência não seja básica
diff --git a/crates/ui-egui/src/i18n/ru.tsv b/crates/ui-egui/src/i18n/ru.tsv
index 367f5f1b..80d8d8c8 100644
--- a/crates/ui-egui/src/i18n/ru.tsv
+++ b/crates/ui-egui/src/i18n/ru.tsv
@@ -3800,6 +3800,8 @@ axis	Both	Оба
 @msg	recovery copy `{file}`: {e}	копия восстановления `{file}`: {e}
 @msg	resolutions must be between 1 and 2400 ppi	разрешения должны быть от 1 до 2400 ppi
 @msg	result would exceed the canvas (coordinates out of range)	результат превысил бы холст (координаты вне диапазона)
+@msg	objects can't be nested more than 32 deep	объекты нельзя вкладывать глубже 32 уровней
+@msg	the SVG's elements are nested more than {0} deep	элементы SVG вложены глубже {0} уровней
 @msg	scale must be a number from {_1} to {_2}, not {_3}	масштаб должен быть числом от {_1} до {_2}, а не {_3}
 @msg	scale must be a number from {_1} to {_2}, not {s}	масштаб должен быть числом от {_1} до {_2}, а не {s}
 @msg	select (or target) objects whose appearance isn't basic	выделите (или укажите как объект) объекты, оформление которых не является основным
diff --git a/crates/ui-egui/src/i18n/uk.tsv b/crates/ui-egui/src/i18n/uk.tsv
index 1791565a..82efe7e1 100644
--- a/crates/ui-egui/src/i18n/uk.tsv
+++ b/crates/ui-egui/src/i18n/uk.tsv
@@ -3788,6 +3788,8 @@ axis	Both	Обидві
 @msg	recovery copy `{file}`: {e}	копія відновлення `{file}`: {e}
 @msg	resolutions must be between 1 and 2400 ppi	дозволи мають бути від 1 до 2400 ppi
 @msg	result would exceed the canvas (coordinates out of range)	результат перевищив би полотно (координати поза діапазоном)
+@msg	objects can't be nested more than 32 deep	об’єкти не можна вкладати глибше ніж на 32 рівні
+@msg	the SVG's elements are nested more than {0} deep	елементи SVG вкладено глибше ніж на {0} рівнів
 @msg	scale must be a number from {_1} to {_2}, not {_3}	масштаб має бути числом від {_1} до {_2}, а не {_3}
 @msg	scale must be a number from {_1} to {_2}, not {s}	масштаб має бути числом від {_1} до {_2}, а не {s}
 @msg	select (or target) objects whose appearance isn't basic	виділіть (або вкажіть як об’єкт) об’єкти, оформлення яких не є основним
diff --git a/crates/ui-egui/src/i18n/vi.tsv b/crates/ui-egui/src/i18n/vi.tsv
index d2e8d3ea..a9c00b35 100644
--- a/crates/ui-egui/src/i18n/vi.tsv
+++ b/crates/ui-egui/src/i18n/vi.tsv
@@ -4071,6 +4071,8 @@ theme	Appearance	Giao diện
 @msg	resolutions must be between 1 and 2400 ppi	độ phân giải phải nằm trong khoảng 1 đến 2400 ppi
 @msg	Restored {_1} recovered document(s): save them to keep them	Đã phục hồi {_1} tài liệu: hãy lưu để giữ lại
 @msg	result would exceed the canvas (coordinates out of range)	kết quả sẽ vượt quá vùng vẽ (tọa độ ngoài phạm vi)
+@msg	objects can't be nested more than 32 deep	không thể lồng các đối tượng sâu quá 32 cấp
+@msg	the SVG's elements are nested more than {0} deep	các phần tử SVG lồng nhau sâu quá {0} cấp
 @msg	Save for Web: the image is empty	Lưu cho Web: ảnh trống
 @msg	Save writes {_1}, not {_2}: use document.export for other formats	Lưu ghi {_1}, không phải {_2}: dùng document.export cho các định dạng khác
 @msg	saved panel layout is invalid; reset the workspace first	bố cục bảng đã lưu không hợp lệ; hãy đặt lại không gian làm việc trước