Move layout traits into library

16 files changed, 734 insertions, 1713 deletions

diff --git a/src/model/capture.rs b/src/model/capture.rs
deleted file mode 100644
index c4c107b2..00000000
--- a/src/model/capture.rs
+++ /dev/null
@@ -1,186 +0,0 @@
-use super::{Scope, Scopes, Value};
-use crate::syntax::ast::TypedNode;
-use crate::syntax::{ast, SyntaxNode};
-
-/// A visitor that captures variable slots.
-pub struct CapturesVisitor<'a> {
-    external: &'a Scopes<'a>,
-    internal: Scopes<'a>,
-    captures: Scope,
-}
-
-impl<'a> CapturesVisitor<'a> {
-    /// Create a new visitor for the given external scopes.
-    pub fn new(external: &'a Scopes) -> Self {
-        Self {
-            external,
-            internal: Scopes::new(None),
-            captures: Scope::new(),
-        }
-    }
-
-    /// Return the scope of captured variables.
-    pub fn finish(self) -> Scope {
-        self.captures
-    }
-
-    /// Bind a new internal variable.
-    pub fn bind(&mut self, ident: ast::Ident) {
-        self.internal.top.define(ident.take(), Value::None);
-    }
-
-    /// Capture a variable if it isn't internal.
-    pub fn capture(&mut self, ident: ast::Ident) {
-        if self.internal.get(&ident).is_err() {
-            if let Ok(value) = self.external.get(&ident) {
-                self.captures.define_captured(ident.take(), value.clone());
-            }
-        }
-    }
-
-    /// Visit any node and collect all captured variables.
-    pub fn visit(&mut self, node: &SyntaxNode) {
-        match node.cast() {
-            // Every identifier is a potential variable that we need to capture.
-            // Identifiers that shouldn't count as captures because they
-            // actually bind a new name are handled below (individually through
-            // the expressions that contain them).
-            Some(ast::Expr::Ident(ident)) => self.capture(ident),
-
-            // Code and content blocks create a scope.
-            Some(ast::Expr::Code(_) | ast::Expr::Content(_)) => {
-                self.internal.enter();
-                for child in node.children() {
-                    self.visit(child);
-                }
-                self.internal.exit();
-            }
-
-            // A closure contains parameter bindings, which are bound before the
-            // body is evaluated. Care must be taken so that the default values
-            // of named parameters cannot access previous parameter bindings.
-            Some(ast::Expr::Closure(expr)) => {
-                for param in expr.params() {
-                    if let ast::Param::Named(named) = param {
-                        self.visit(named.expr().as_untyped());
-                    }
-                }
-
-                for param in expr.params() {
-                    match param {
-                        ast::Param::Pos(ident) => self.bind(ident),
-                        ast::Param::Named(named) => self.bind(named.name()),
-                        ast::Param::Sink(ident) => self.bind(ident),
-                    }
-                }
-
-                self.visit(expr.body().as_untyped());
-            }
-
-            // A let expression contains a binding, but that binding is only
-            // active after the body is evaluated.
-            Some(ast::Expr::Let(expr)) => {
-                if let Some(init) = expr.init() {
-                    self.visit(init.as_untyped());
-                }
-                self.bind(expr.binding());
-            }
-
-            // A show rule contains a binding, but that binding is only active
-            // after the target has been evaluated.
-            Some(ast::Expr::Show(show)) => {
-                self.visit(show.pattern().as_untyped());
-                if let Some(binding) = show.binding() {
-                    self.bind(binding);
-                }
-                self.visit(show.body().as_untyped());
-            }
-
-            // A for loop contains one or two bindings in its pattern. These are
-            // active after the iterable is evaluated but before the body is
-            // evaluated.
-            Some(ast::Expr::For(expr)) => {
-                self.visit(expr.iter().as_untyped());
-                let pattern = expr.pattern();
-                if let Some(key) = pattern.key() {
-                    self.bind(key);
-                }
-                self.bind(pattern.value());
-                self.visit(expr.body().as_untyped());
-            }
-
-            // An import contains items, but these are active only after the
-            // path is evaluated.
-            Some(ast::Expr::Import(expr)) => {
-                self.visit(expr.path().as_untyped());
-                if let ast::Imports::Items(items) = expr.imports() {
-                    for item in items {
-                        self.bind(item);
-                    }
-                }
-            }
-
-            // Everything else is traversed from left to right.
-            _ => {
-                for child in node.children() {
-                    self.visit(child);
-                }
-            }
-        }
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::syntax::parse;
-
-    #[track_caller]
-    fn test(text: &str, result: &[&str]) {
-        let mut scopes = Scopes::new(None);
-        scopes.top.define("x", 0);
-        scopes.top.define("y", 0);
-        scopes.top.define("z", 0);
-
-        let mut visitor = CapturesVisitor::new(&scopes);
-        let root = parse(text);
-        visitor.visit(&root);
-
-        let captures = visitor.finish();
-        let mut names: Vec<_> = captures.iter().map(|(k, _)| k).collect();
-        names.sort();
-
-        assert_eq!(names, result);
-    }
-
-    #[test]
-    fn test_captures() {
-        // Let binding and function definition.
-        test("#let x = x", &["x"]);
-        test("#let x; {x + y}", &["y"]);
-        test("#let f(x, y) = x + y", &[]);
-
-        // Closure with different kinds of params.
-        test("{(x, y) => x + z}", &["z"]);
-        test("{(x: y, z) => x + z}", &["y"]);
-        test("{(..x) => x + y}", &["y"]);
-        test("{(x, y: x + z) => x + y}", &["x", "z"]);
-
-        // Show rule.
-        test("#show x: y as x", &["y"]);
-        test("#show x: y as x + z", &["y", "z"]);
-        test("#show x: x as x", &["x"]);
-
-        // For loop.
-        test("#for x in y { x + z }", &["y", "z"]);
-        test("#for x, y in y { x + y }", &["y"]);
-
-        // Import.
-        test("#import x, y from z", &["z"]);
-        test("#import x, y, z from x + y", &["x", "y"]);
-
-        // Blocks.
-        test("{ let x = 1; { let y = 2; y }; x + y }", &["y"]);
-        test("[#let x = 1]#x", &["x"]);
-    }
-}
diff --git a/src/model/collapse.rs b/src/model/collapse.rs
deleted file mode 100644
index f57a3a42..00000000
--- a/src/model/collapse.rs
+++ /dev/null
@@ -1,116 +0,0 @@
-use super::{StyleChain, StyleVec, StyleVecBuilder};
-
-/// A wrapper around a [`StyleVecBuilder`] that allows to collapse items.
-pub(super) struct CollapsingBuilder<'a, T> {
-    /// The internal builder.
-    builder: StyleVecBuilder<'a, T>,
-    /// Staged weak and ignorant items that we can't yet commit to the builder.
-    /// The option is `Some(_)` for weak items and `None` for ignorant items.
-    staged: Vec<(T, StyleChain<'a>, Option<u8>)>,
-    /// What the last non-ignorant item was.
-    last: Last,
-}
-
-/// What the last non-ignorant item was.
-#[derive(Debug, Copy, Clone, Eq, PartialEq)]
-enum Last {
-    Weak,
-    Destructive,
-    Supportive,
-}
-
-impl<'a, T> CollapsingBuilder<'a, T> {
-    /// Create a new style-vec builder.
-    pub fn new() -> Self {
-        Self {
-            builder: StyleVecBuilder::new(),
-            staged: vec![],
-            last: Last::Destructive,
-        }
-    }
-
-    /// Whether the builder is empty.
-    pub fn is_empty(&self) -> bool {
-        self.builder.is_empty() && self.staged.is_empty()
-    }
-
-    /// Can only exist when there is at least one supportive item to its left
-    /// and to its right, with no destructive items in between. There may be
-    /// ignorant items in between in both directions.
-    ///
-    /// Between weak items, there may be at least one per layer and among the
-    /// candidates the strongest one (smallest `weakness`) wins. When tied,
-    /// the one that compares larger through `PartialOrd` wins.
-    pub fn weak(&mut self, item: T, styles: StyleChain<'a>, weakness: u8)
-    where
-        T: PartialOrd,
-    {
-        if self.last == Last::Destructive {
-            return;
-        }
-
-        if self.last == Last::Weak {
-            if let Some(i) =
-                self.staged.iter().position(|(prev_item, _, prev_weakness)| {
-                    prev_weakness.map_or(false, |prev_weakness| {
-                        weakness < prev_weakness
-                            || (weakness == prev_weakness && item > *prev_item)
-                    })
-                })
-            {
-                self.staged.remove(i);
-            } else {
-                return;
-            }
-        }
-
-        self.staged.push((item, styles, Some(weakness)));
-        self.last = Last::Weak;
-    }
-
-    /// Forces nearby weak items to collapse.
-    pub fn destructive(&mut self, item: T, styles: StyleChain<'a>) {
-        self.flush(false);
-        self.builder.push(item, styles);
-        self.last = Last::Destructive;
-    }
-
-    /// Allows nearby weak items to exist.
-    pub fn supportive(&mut self, item: T, styles: StyleChain<'a>) {
-        self.flush(true);
-        self.builder.push(item, styles);
-        self.last = Last::Supportive;
-    }
-
-    /// Has no influence on other items.
-    pub fn ignorant(&mut self, item: T, styles: StyleChain<'a>) {
-        self.staged.push((item, styles, None));
-    }
-
-    /// Iterate over the contained items.
-    pub fn items(&self) -> impl DoubleEndedIterator<Item = &T> {
-        self.builder.items().chain(self.staged.iter().map(|(item, ..)| item))
-    }
-
-    /// Return the finish style vec and the common prefix chain.
-    pub fn finish(mut self) -> (StyleVec<T>, StyleChain<'a>) {
-        self.flush(false);
-        self.builder.finish()
-    }
-
-    /// Push the staged items, filtering out weak items if `supportive` is
-    /// false.
-    fn flush(&mut self, supportive: bool) {
-        for (item, styles, meta) in self.staged.drain(..) {
-            if supportive || meta.is_none() {
-                self.builder.push(item, styles);
-            }
-        }
-    }
-}
-
-impl<'a, T> Default for CollapsingBuilder<'a, T> {
-    fn default() -> Self {
-        Self::new()
-    }
-}
diff --git a/src/model/content.rs b/src/model/content.rs
index 170d47a1..1cffa773 100644
--- a/src/model/content.rs
+++ b/src/model/content.rs
@@ -5,18 +5,12 @@ use std::iter::{self, Sum};
 use std::ops::{Add, AddAssign};
 use std::sync::Arc;
 
-use comemo::Tracked;
 use siphasher::sip128::{Hasher128, SipHasher};
 use typst_macros::node;
 
-use super::{
-    Args, Barrier, Builder, Key, Layout, Level, Property, Regions, Scratch, Selector,
-    StyleChain, StyleEntry, StyleMap, Vm,
-};
+use super::{Args, Key, Property, Selector, StyleEntry, StyleMap, Vm};
 use crate::diag::{SourceResult, StrResult};
-use crate::frame::Frame;
 use crate::util::ReadableTypeId;
-use crate::World;
 
 /// Composable representation of styled content.
 ///
@@ -40,22 +34,27 @@ impl Content {
         }
     }
 
+    /// Whether the content is empty.
     pub fn is_empty(&self) -> bool {
         self.downcast::<SequenceNode>().map_or(false, |seq| seq.0.is_empty())
     }
 
+    /// The id of the contained node.
     pub fn id(&self) -> NodeId {
         (*self.0).id()
     }
 
+    /// Whether the contained node is of type `T`.
     pub fn is<T: 'static>(&self) -> bool {
         (*self.0).as_any().is::<T>()
     }
 
+    /// Cast to `T` if the contained node is of type `T`.
     pub fn downcast<T: 'static>(&self) -> Option<&T> {
         (*self.0).as_any().downcast_ref::<T>()
     }
 
+    /// Try to cast to a mutable instance of `T`.
     fn try_downcast_mut<T: 'static>(&mut self) -> Option<&mut T> {
         Arc::get_mut(&mut self.0)?.as_any_mut().downcast_mut::<T>()
     }
@@ -120,51 +119,6 @@ impl Content {
     pub fn unguard(&self, sel: Selector) -> Self {
         self.clone().styled_with_entry(StyleEntry::Unguard(sel))
     }
-
-    #[comemo::memoize]
-    pub fn layout_block(
-        &self,
-        world: Tracked<dyn World>,
-        regions: &Regions,
-        styles: StyleChain,
-    ) -> SourceResult<Vec<Frame>> {
-        let barrier = StyleEntry::Barrier(Barrier::new(self.id()));
-        let styles = barrier.chain(&styles);
-
-        if let Some(node) = self.to::<dyn Layout>() {
-            if node.level() == Level::Block {
-                return node.layout(world, regions, styles);
-            }
-        }
-
-        let scratch = Scratch::default();
-        let mut builder = Builder::new(world, &scratch, false);
-        builder.accept(self, styles)?;
-        let (flow, shared) = builder.into_flow(styles)?;
-        flow.layout(world, regions, shared)
-    }
-
-
-    #[comemo::memoize]
-    pub fn layout_inline(
-        &self,
-        world: Tracked<dyn World>,
-        regions: &Regions,
-        styles: StyleChain,
-    ) -> SourceResult<Vec<Frame>> {
-        let barrier = StyleEntry::Barrier(Barrier::new(self.id()));
-        let styles = barrier.chain(&styles);
-
-        if let Some(node) = self.to::<dyn Layout>() {
-            return node.layout(world, regions, styles);
-        }
-
-        let scratch = Scratch::default();
-        let mut builder = Builder::new(world, &scratch, false);
-        builder.accept(self, styles)?;
-        let (flow, shared) = builder.into_flow(styles)?;
-        flow.layout(world, regions, shared)
-    }
 }
 
 impl Default for Content {
@@ -293,6 +247,11 @@ pub trait Node: 'static {
     fn vtable(&self, id: TypeId) -> Option<*const ()>;
 }
 
+/// A capability a node can have.
+///
+/// This is implemented by trait objects.
+pub trait Capability: 'static + Send + Sync {}
+
 /// A unique identifier for a node.
 #[derive(Copy, Clone, Eq, PartialEq, Hash)]
 pub struct NodeId(ReadableTypeId);
@@ -310,15 +269,12 @@ impl Debug for NodeId {
     }
 }
 
-/// A capability a node can have.
-///
-/// This is implemented by trait objects.
-pub trait Capability: 'static + Send + Sync {}
-
 /// A node with applied styles.
 #[derive(Clone, Hash)]
 pub struct StyledNode {
+    /// The styled content.
     pub sub: Content,
+    /// The styles.
     pub map: StyleMap,
 }
 
diff --git a/src/model/fold.rs b/src/model/fold.rs
deleted file mode 100644
index bc85be01..00000000
--- a/src/model/fold.rs
+++ /dev/null
@@ -1,81 +0,0 @@
-use super::Smart;
-use crate::geom::{Abs, Corners, Length, Rel, Sides};
-
-/// A property that is folded to determine its final value.
-pub trait Fold {
-    /// The type of the folded output.
-    type Output;
-
-    /// Fold this inner value with an outer folded value.
-    fn fold(self, outer: Self::Output) -> Self::Output;
-}
-
-impl<T> Fold for Option<T>
-where
-    T: Fold,
-    T::Output: Default,
-{
-    type Output = Option<T::Output>;
-
-    fn fold(self, outer: Self::Output) -> Self::Output {
-        self.map(|inner| inner.fold(outer.unwrap_or_default()))
-    }
-}
-
-impl<T> Fold for Smart<T>
-where
-    T: Fold,
-    T::Output: Default,
-{
-    type Output = Smart<T::Output>;
-
-    fn fold(self, outer: Self::Output) -> Self::Output {
-        self.map(|inner| inner.fold(outer.unwrap_or_default()))
-    }
-}
-
-impl<T> Fold for Sides<T>
-where
-    T: Fold,
-{
-    type Output = Sides<T::Output>;
-
-    fn fold(self, outer: Self::Output) -> Self::Output {
-        self.zip(outer, |inner, outer| inner.fold(outer))
-    }
-}
-
-impl Fold for Sides<Option<Rel<Abs>>> {
-    type Output = Sides<Rel<Abs>>;
-
-    fn fold(self, outer: Self::Output) -> Self::Output {
-        self.zip(outer, |inner, outer| inner.unwrap_or(outer))
-    }
-}
-
-impl Fold for Sides<Option<Smart<Rel<Length>>>> {
-    type Output = Sides<Smart<Rel<Length>>>;
-
-    fn fold(self, outer: Self::Output) -> Self::Output {
-        self.zip(outer, |inner, outer| inner.unwrap_or(outer))
-    }
-}
-
-impl<T> Fold for Corners<T>
-where
-    T: Fold,
-{
-    type Output = Corners<T::Output>;
-
-    fn fold(self, outer: Self::Output) -> Self::Output {
-        self.zip(outer, |inner, outer| inner.fold(outer))
-    }
-}
-
-impl Fold for Corners<Option<Rel<Abs>>> {
-    type Output = Corners<Rel<Abs>>;
-
-    fn fold(self, outer: Self::Output) -> Self::Output {
-        self.zip(outer, |inner, outer| inner.unwrap_or(outer))
-    }
-}
diff --git a/src/model/func.rs b/src/model/func.rs
index 47ad4436..dff58233 100644
--- a/src/model/func.rs
+++ b/src/model/func.rs
@@ -6,8 +6,8 @@ use comemo::{Track, Tracked};
 
 use super::{Args, Eval, Flow, Node, NodeId, Route, Scope, Scopes, StyleMap, Value, Vm};
 use crate::diag::{SourceResult, StrResult};
-use crate::syntax::ast::Expr;
-use crate::syntax::SourceId;
+use crate::syntax::ast::{self, Expr, TypedNode};
+use crate::syntax::{SourceId, SyntaxNode};
 use crate::util::EcoString;
 use crate::World;
 
@@ -227,3 +227,186 @@ impl Closure {
         result
     }
 }
+
+/// A visitor that determines which variables to capture for a closure.
+pub struct CapturesVisitor<'a> {
+    external: &'a Scopes<'a>,
+    internal: Scopes<'a>,
+    captures: Scope,
+}
+
+impl<'a> CapturesVisitor<'a> {
+    /// Create a new visitor for the given external scopes.
+    pub fn new(external: &'a Scopes) -> Self {
+        Self {
+            external,
+            internal: Scopes::new(None),
+            captures: Scope::new(),
+        }
+    }
+
+    /// Return the scope of captured variables.
+    pub fn finish(self) -> Scope {
+        self.captures
+    }
+
+    /// Bind a new internal variable.
+    pub fn bind(&mut self, ident: ast::Ident) {
+        self.internal.top.define(ident.take(), Value::None);
+    }
+
+    /// Capture a variable if it isn't internal.
+    pub fn capture(&mut self, ident: ast::Ident) {
+        if self.internal.get(&ident).is_err() {
+            if let Ok(value) = self.external.get(&ident) {
+                self.captures.define_captured(ident.take(), value.clone());
+            }
+        }
+    }
+
+    /// Visit any node and collect all captured variables.
+    pub fn visit(&mut self, node: &SyntaxNode) {
+        match node.cast() {
+            // Every identifier is a potential variable that we need to capture.
+            // Identifiers that shouldn't count as captures because they
+            // actually bind a new name are handled below (individually through
+            // the expressions that contain them).
+            Some(ast::Expr::Ident(ident)) => self.capture(ident),
+
+            // Code and content blocks create a scope.
+            Some(ast::Expr::Code(_) | ast::Expr::Content(_)) => {
+                self.internal.enter();
+                for child in node.children() {
+                    self.visit(child);
+                }
+                self.internal.exit();
+            }
+
+            // A closure contains parameter bindings, which are bound before the
+            // body is evaluated. Care must be taken so that the default values
+            // of named parameters cannot access previous parameter bindings.
+            Some(ast::Expr::Closure(expr)) => {
+                for param in expr.params() {
+                    if let ast::Param::Named(named) = param {
+                        self.visit(named.expr().as_untyped());
+                    }
+                }
+
+                for param in expr.params() {
+                    match param {
+                        ast::Param::Pos(ident) => self.bind(ident),
+                        ast::Param::Named(named) => self.bind(named.name()),
+                        ast::Param::Sink(ident) => self.bind(ident),
+                    }
+                }
+
+                self.visit(expr.body().as_untyped());
+            }
+
+            // A let expression contains a binding, but that binding is only
+            // active after the body is evaluated.
+            Some(ast::Expr::Let(expr)) => {
+                if let Some(init) = expr.init() {
+                    self.visit(init.as_untyped());
+                }
+                self.bind(expr.binding());
+            }
+
+            // A show rule contains a binding, but that binding is only active
+            // after the target has been evaluated.
+            Some(ast::Expr::Show(show)) => {
+                self.visit(show.pattern().as_untyped());
+                if let Some(binding) = show.binding() {
+                    self.bind(binding);
+                }
+                self.visit(show.body().as_untyped());
+            }
+
+            // A for loop contains one or two bindings in its pattern. These are
+            // active after the iterable is evaluated but before the body is
+            // evaluated.
+            Some(ast::Expr::For(expr)) => {
+                self.visit(expr.iter().as_untyped());
+                let pattern = expr.pattern();
+                if let Some(key) = pattern.key() {
+                    self.bind(key);
+                }
+                self.bind(pattern.value());
+                self.visit(expr.body().as_untyped());
+            }
+
+            // An import contains items, but these are active only after the
+            // path is evaluated.
+            Some(ast::Expr::Import(expr)) => {
+                self.visit(expr.path().as_untyped());
+                if let ast::Imports::Items(items) = expr.imports() {
+                    for item in items {
+                        self.bind(item);
+                    }
+                }
+            }
+
+            // Everything else is traversed from left to right.
+            _ => {
+                for child in node.children() {
+                    self.visit(child);
+                }
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::syntax::parse;
+
+    #[track_caller]
+    fn test(text: &str, result: &[&str]) {
+        let mut scopes = Scopes::new(None);
+        scopes.top.define("x", 0);
+        scopes.top.define("y", 0);
+        scopes.top.define("z", 0);
+
+        let mut visitor = CapturesVisitor::new(&scopes);
+        let root = parse(text);
+        visitor.visit(&root);
+
+        let captures = visitor.finish();
+        let mut names: Vec<_> = captures.iter().map(|(k, _)| k).collect();
+        names.sort();
+
+        assert_eq!(names, result);
+    }
+
+    #[test]
+    fn test_captures() {
+        // Let binding and function definition.
+        test("#let x = x", &["x"]);
+        test("#let x; {x + y}", &["y"]);
+        test("#let f(x, y) = x + y", &[]);
+
+        // Closure with different kinds of params.
+        test("{(x, y) => x + z}", &["z"]);
+        test("{(x: y, z) => x + z}", &["y"]);
+        test("{(..x) => x + y}", &["y"]);
+        test("{(x, y: x + z) => x + y}", &["x", "z"]);
+
+        // Show rule.
+        test("#show x: y as x", &["y"]);
+        test("#show x: y as x + z", &["y", "z"]);
+        test("#show x: x as x", &["x"]);
+
+        // For loop.
+        test("#for x in y { x + z }", &["y", "z"]);
+        test("#for x, y in y { x + y }", &["y"]);
+
+        // Import.
+        test("#import x, y from z", &["z"]);
+        test("#import x, y, z from x + y", &["x", "y"]);
+
+        // Blocks.
+        test("{ let x = 1; { let y = 2; y }; x + y }", &["y"]);
+        test("[#let x = 1]#x", &["x"]);
+    }
+}
diff --git a/src/model/layout.rs b/src/model/layout.rs
deleted file mode 100644
index e8aa0e96..00000000
--- a/src/model/layout.rs
+++ /dev/null
@@ -1,142 +0,0 @@
-//! Layouting infrastructure.
-
-use std::hash::Hash;
-
-use comemo::Tracked;
-
-use super::{Builder, Capability, Content, Scratch, StyleChain};
-use crate::diag::SourceResult;
-use crate::frame::Frame;
-use crate::geom::{Abs, Axes, Size};
-use crate::World;
-
-/// Layout content into a collection of pages.
-#[comemo::memoize]
-pub fn layout(world: Tracked<dyn World>, content: &Content) -> SourceResult<Vec<Frame>> {
-    let styles = StyleChain::with_root(&world.config().styles);
-    let scratch = Scratch::default();
-
-    let mut builder = Builder::new(world, &scratch, true);
-    builder.accept(content, styles)?;
-
-    let (doc, shared) = builder.into_doc(styles)?;
-    doc.layout(world, shared)
-}
-
-/// A node that can be layouted into a sequence of regions.
-///
-/// Layouting returns one frame per used region.
-pub trait Layout: 'static + Sync + Send {
-    /// Layout this node into the given regions, producing frames.
-    fn layout(
-        &self,
-        world: Tracked<dyn World>,
-        regions: &Regions,
-        styles: StyleChain,
-    ) -> SourceResult<Vec<Frame>>;
-
-    /// Whether this is an inline-level or block-level node.
-    fn level(&self) -> Level;
-}
-
-impl Capability for dyn Layout {}
-
-/// At which level a node operates.
-#[derive(Debug, Copy, Clone, Eq, PartialEq)]
-pub enum Level {
-    Inline,
-    Block,
-}
-
-/// A sequence of regions to layout into.
-#[derive(Debug, Clone, Hash)]
-pub struct Regions {
-    /// The (remaining) size of the first region.
-    pub first: Size,
-    /// The base size for relative sizing.
-    pub base: Size,
-    /// The height of followup regions. The width is the same for all regions.
-    pub backlog: Vec<Abs>,
-    /// The height of the final region that is repeated once the backlog is
-    /// drained. The width is the same for all regions.
-    pub last: Option<Abs>,
-    /// Whether nodes should expand to fill the regions instead of shrinking to
-    /// fit the content.
-    pub expand: Axes<bool>,
-}
-
-impl Regions {
-    /// Create a new region sequence with exactly one region.
-    pub fn one(size: Size, base: Size, expand: Axes<bool>) -> Self {
-        Self {
-            first: size,
-            base,
-            backlog: vec![],
-            last: None,
-            expand,
-        }
-    }
-
-    /// Create a new sequence of same-size regions that repeats indefinitely.
-    pub fn repeat(size: Size, base: Size, expand: Axes<bool>) -> Self {
-        Self {
-            first: size,
-            base,
-            backlog: vec![],
-            last: Some(size.y),
-            expand,
-        }
-    }
-
-    /// Create new regions where all sizes are mapped with `f`.
-    ///
-    /// Note that since all regions must have the same width, the width returned
-    /// by `f` is ignored for the backlog and the final region.
-    pub fn map<F>(&self, mut f: F) -> Self
-    where
-        F: FnMut(Size) -> Size,
-    {
-        let x = self.first.x;
-        Self {
-            first: f(self.first),
-            base: f(self.base),
-            backlog: self.backlog.iter().map(|&y| f(Size::new(x, y)).y).collect(),
-            last: self.last.map(|y| f(Size::new(x, y)).y),
-            expand: self.expand,
-        }
-    }
-
-    /// Whether the first region is full and a region break is called for.
-    pub fn is_full(&self) -> bool {
-        Abs::zero().fits(self.first.y) && !self.in_last()
-    }
-
-    /// Whether the first region is the last usable region.
-    ///
-    /// If this is true, calling `next()` will have no effect.
-    pub fn in_last(&self) -> bool {
-        self.backlog.len() == 0 && self.last.map_or(true, |height| self.first.y == height)
-    }
-
-    /// Advance to the next region if there is any.
-    pub fn next(&mut self) {
-        if let Some(height) = (!self.backlog.is_empty())
-            .then(|| self.backlog.remove(0))
-            .or(self.last)
-        {
-            self.first.y = height;
-            self.base.y = height;
-        }
-    }
-
-    /// An iterator that returns the sizes of the first and all following
-    /// regions, equivalently to what would be produced by calling
-    /// [`next()`](Self::next) repeatedly until all regions are exhausted.
-    /// This iterater may be infinite.
-    pub fn iter(&self) -> impl Iterator<Item = Size> + '_ {
-        let first = std::iter::once(self.first);
-        let backlog = self.backlog.iter();
-        let last = self.last.iter().cycle();
-        first.chain(backlog.chain(last).map(|&h| Size::new(self.first.x, h)))
-    }
-}
diff --git a/src/model/mod.rs b/src/model/mod.rs
index aba9514c..b4f8f653 100644
--- a/src/model/mod.rs
+++ b/src/model/mod.rs
@@ -1,14 +1,6 @@
 //! Layout and computation model.
 
 #[macro_use]
-mod styles;
-mod collapse;
-mod content;
-mod eval;
-mod layout;
-mod property;
-mod recipe;
-#[macro_use]
 mod cast;
 #[macro_use]
 mod array;
@@ -18,38 +10,29 @@ mod dict;
 mod str;
 #[macro_use]
 mod value;
+#[macro_use]
+mod styles;
 mod args;
-mod capture;
-mod fold;
+mod content;
+mod eval;
 mod func;
-pub mod methods;
-pub mod ops;
-mod raw;
-mod realize;
-mod resolve;
 mod scope;
 mod vm;
 
+pub mod methods;
+pub mod ops;
+
 pub use self::str::*;
 pub use args::*;
 pub use array::*;
-pub use capture::*;
 pub use cast::*;
 pub use content::*;
 pub use dict::*;
 pub use eval::*;
-pub use fold::*;
 pub use func::*;
-pub use layout::*;
-pub use property::*;
-pub use raw::*;
-pub use recipe::*;
-pub use resolve::*;
 pub use scope::*;
 pub use styles::*;
-pub use typst_macros::node;
 pub use value::*;
 pub use vm::*;
 
-// use collapse::*;
-use realize::*;
+pub use typst_macros::{capability, node};
diff --git a/src/model/ops.rs b/src/model/ops.rs
index 7a8c6950..7eb814c1 100644
--- a/src/model/ops.rs
+++ b/src/model/ops.rs
@@ -2,10 +2,11 @@
 
 use std::cmp::Ordering;
 
-use super::{Node, RawAlign, RawStroke, Regex, Smart, Value};
+use super::{Node, Regex, Smart, Value};
 use crate::diag::StrResult;
 use crate::geom::{Axes, Axis, Length, Numeric, Rel};
 use crate::library::text::TextNode;
+use crate::library::{RawAlign, RawStroke};
 use Value::*;
 
 /// Bail with a type mismatch error.
diff --git a/src/model/property.rs b/src/model/property.rs
deleted file mode 100644
index 3a498d2c..00000000
--- a/src/model/property.rs
+++ /dev/null
@@ -1,195 +0,0 @@
-use std::any::Any;
-use std::fmt::{self, Debug, Formatter};
-use std::hash::Hash;
-use std::sync::Arc;
-
-use comemo::Prehashed;
-
-use super::{Interruption, NodeId, StyleChain};
-use crate::library::layout::PageNode;
-use crate::library::structure::{DescNode, EnumNode, ListNode};
-use crate::library::text::ParNode;
-use crate::util::ReadableTypeId;
-
-/// A style property originating from a set rule or constructor.
-#[derive(Clone, Hash)]
-pub struct Property {
-    /// The id of the property's [key](Key).
-    key: KeyId,
-    /// The id of the node the property belongs to.
-    node: NodeId,
-    /// Whether the property should only affect the first node down the
-    /// hierarchy. Used by constructors.
-    scoped: bool,
-    /// The property's value.
-    value: Arc<Prehashed<dyn Bounds>>,
-    /// The name of the property.
-    #[cfg(debug_assertions)]
-    name: &'static str,
-}
-
-impl Property {
-    /// Create a new property from a key-value pair.
-    pub fn new<'a, K: Key<'a>>(_: K, value: K::Value) -> Self {
-        Self {
-            key: KeyId::of::<K>(),
-            node: K::node(),
-            value: Arc::new(Prehashed::new(value)),
-            scoped: false,
-            #[cfg(debug_assertions)]
-            name: K::NAME,
-        }
-    }
-
-    /// Whether this property has the given key.
-    pub fn is<'a, K: Key<'a>>(&self) -> bool {
-        self.key == KeyId::of::<K>()
-    }
-
-    /// Whether this property belongs to the node `T`.
-    pub fn is_of<T: 'static>(&self) -> bool {
-        self.node == NodeId::of::<T>()
-    }
-
-    /// Access the property's value if it is of the given key.
-    pub fn downcast<'a, K: Key<'a>>(&'a self) -> Option<&'a K::Value> {
-        if self.key == KeyId::of::<K>() {
-            (**self.value).as_any().downcast_ref()
-        } else {
-            None
-        }
-    }
-
-    /// The node this property is for.
-    pub fn node(&self) -> NodeId {
-        self.node
-    }
-
-    /// Whether the property is scoped.
-    pub fn scoped(&self) -> bool {
-        self.scoped
-    }
-
-    /// Make the property scoped.
-    pub fn make_scoped(&mut self) {
-        self.scoped = true;
-    }
-
-    /// What kind of structure the property interrupts.
-    pub fn interruption(&self) -> Option<Interruption> {
-        if self.is_of::<PageNode>() {
-            Some(Interruption::Page)
-        } else if self.is_of::<ParNode>() {
-            Some(Interruption::Par)
-        } else if self.is_of::<ListNode>()
-            || self.is_of::<EnumNode>()
-            || self.is_of::<DescNode>()
-        {
-            Some(Interruption::List)
-        } else {
-            None
-        }
-    }
-}
-
-impl Debug for Property {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        #[cfg(debug_assertions)]
-        write!(f, "{} = ", self.name)?;
-        write!(f, "{:?}", self.value)?;
-        if self.scoped {
-            write!(f, " [scoped]")?;
-        }
-        Ok(())
-    }
-}
-
-impl PartialEq for Property {
-    fn eq(&self, other: &Self) -> bool {
-        self.key == other.key
-            && self.value.eq(&other.value)
-            && self.scoped == other.scoped
-    }
-}
-
-trait Bounds: Debug + Sync + Send + 'static {
-    fn as_any(&self) -> &dyn Any;
-}
-
-impl<T> Bounds for T
-where
-    T: Debug + Sync + Send + 'static,
-{
-    fn as_any(&self) -> &dyn Any {
-        self
-    }
-}
-
-/// A style property key.
-///
-/// This trait is not intended to be implemented manually, but rather through
-/// the `#[node]` proc-macro.
-pub trait Key<'a>: Copy + 'static {
-    /// The unfolded type which this property is stored as in a style map.
-    type Value: Debug + Clone + Hash + Sync + Send + 'static;
-
-    /// The folded type of value that is returned when reading this property
-    /// from a style chain.
-    type Output;
-
-    /// The name of the property, used for debug printing.
-    const NAME: &'static str;
-
-    /// The id of the node the key belongs to.
-    fn node() -> NodeId;
-
-    /// Compute an output value from a sequence of values belonging to this key,
-    /// folding if necessary.
-    fn get(
-        chain: StyleChain<'a>,
-        values: impl Iterator<Item = &'a Self::Value>,
-    ) -> Self::Output;
-}
-
-/// A unique identifier for a property key.
-#[derive(Copy, Clone, Eq, PartialEq, Hash)]
-struct KeyId(ReadableTypeId);
-
-impl KeyId {
-    /// The id of the given key.
-    pub fn of<'a, T: Key<'a>>() -> Self {
-        Self(ReadableTypeId::of::<T>())
-    }
-}
-
-impl Debug for KeyId {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        self.0.fmt(f)
-    }
-}
-
-/// A scoped property barrier.
-///
-/// Barriers interact with [scoped](super::StyleMap::scoped) styles: A scoped
-/// style can still be read through a single barrier (the one of the node it
-/// _should_ apply to), but a second barrier will make it invisible.
-#[derive(Copy, Clone, Eq, PartialEq, Hash)]
-pub struct Barrier(NodeId);
-
-impl Barrier {
-    /// Create a new barrier for the given node.
-    pub fn new(node: NodeId) -> Self {
-        Self(node)
-    }
-
-    /// Whether this barrier is for the node `T`.
-    pub fn is_for(&self, node: NodeId) -> bool {
-        self.0 == node
-    }
-}
-
-impl Debug for Barrier {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        write!(f, "Barrier for {:?}", self.0)
-    }
-}
diff --git a/src/model/raw.rs b/src/model/raw.rs
deleted file mode 100644
index b9242b51..00000000
--- a/src/model/raw.rs
+++ /dev/null
@@ -1,149 +0,0 @@
-use std::fmt::{self, Debug, Formatter};
-
-use super::{Fold, Resolve, Smart, StyleChain, Value};
-use crate::geom::{Abs, Align, Axes, Axis, Get, Length, Paint, Stroke};
-use crate::library::text::TextNode;
-
-/// The unresolved alignment representation.
-#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
-pub enum RawAlign {
-    /// Align at the start side of the text direction.
-    Start,
-    /// Align at the end side of the text direction.
-    End,
-    /// Align at a specific alignment.
-    Specific(Align),
-}
-
-impl Resolve for RawAlign {
-    type Output = Align;
-
-    fn resolve(self, styles: StyleChain) -> Self::Output {
-        let dir = styles.get(TextNode::DIR);
-        match self {
-            Self::Start => dir.start().into(),
-            Self::End => dir.end().into(),
-            Self::Specific(align) => align,
-        }
-    }
-}
-
-impl RawAlign {
-    /// The axis this alignment belongs to.
-    pub const fn axis(self) -> Axis {
-        match self {
-            Self::Start | Self::End => Axis::X,
-            Self::Specific(align) => align.axis(),
-        }
-    }
-}
-
-impl From<Align> for RawAlign {
-    fn from(align: Align) -> Self {
-        Self::Specific(align)
-    }
-}
-
-impl Debug for RawAlign {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        match self {
-            Self::Start => f.pad("start"),
-            Self::End => f.pad("end"),
-            Self::Specific(align) => align.fmt(f),
-        }
-    }
-}
-
-dynamic! {
-    RawAlign: "alignment",
-}
-
-dynamic! {
-    Axes<RawAlign>: "2d alignment",
-}
-
-castable! {
-    Axes<Option<RawAlign>>,
-    Expected: "1d or 2d alignment",
-    @align: RawAlign => {
-        let mut aligns = Axes::default();
-        aligns.set(align.axis(), Some(*align));
-        aligns
-    },
-    @aligns: Axes<RawAlign> => aligns.map(Some),
-}
-
-/// The unresolved stroke representation.
-///
-/// In this representation, both fields are optional so that you can pass either
-/// just a paint (`red`), just a thickness (`0.1em`) or both (`2pt + red`) where
-/// this is expected.
-#[derive(Default, Copy, Clone, Eq, PartialEq, Hash)]
-pub struct RawStroke<T = Length> {
-    /// The stroke's paint.
-    pub paint: Smart<Paint>,
-    /// The stroke's thickness.
-    pub thickness: Smart<T>,
-}
-
-impl RawStroke<Abs> {
-    /// Unpack the stroke, filling missing fields from the `default`.
-    pub fn unwrap_or(self, default: Stroke) -> Stroke {
-        Stroke {
-            paint: self.paint.unwrap_or(default.paint),
-            thickness: self.thickness.unwrap_or(default.thickness),
-        }
-    }
-
-    /// Unpack the stroke, filling missing fields with the default values.
-    pub fn unwrap_or_default(self) -> Stroke {
-        self.unwrap_or(Stroke::default())
-    }
-}
-
-impl Resolve for RawStroke {
-    type Output = RawStroke<Abs>;
-
-    fn resolve(self, styles: StyleChain) -> Self::Output {
-        RawStroke {
-            paint: self.paint,
-            thickness: self.thickness.resolve(styles),
-        }
-    }
-}
-
-impl Fold for RawStroke<Abs> {
-    type Output = Self;
-
-    fn fold(self, outer: Self::Output) -> Self::Output {
-        Self {
-            paint: self.paint.or(outer.paint),
-            thickness: self.thickness.or(outer.thickness),
-        }
-    }
-}
-
-impl<T: Debug> Debug for RawStroke<T> {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        match (self.paint, &self.thickness) {
-            (Smart::Custom(paint), Smart::Custom(thickness)) => {
-                write!(f, "{thickness:?} + {paint:?}")
-            }
-            (Smart::Custom(paint), Smart::Auto) => paint.fmt(f),
-            (Smart::Auto, Smart::Custom(thickness)) => thickness.fmt(f),
-            (Smart::Auto, Smart::Auto) => f.pad("<stroke>"),
-        }
-    }
-}
-
-dynamic! {
-    RawStroke: "stroke",
-    Value::Length(thickness) => Self {
-        paint: Smart::Auto,
-        thickness: Smart::Custom(thickness),
-    },
-    Value::Color(color) => Self {
-        paint: Smart::Custom(color.into()),
-        thickness: Smart::Auto,
-    },
-}
diff --git a/src/model/realize.rs b/src/model/realize.rs
deleted file mode 100644
index a99abdd3..00000000
--- a/src/model/realize.rs
+++ /dev/null
@@ -1,486 +0,0 @@
-use std::mem;
-
-use comemo::Tracked;
-use typed_arena::Arena;
-
-use super::collapse::CollapsingBuilder;
-use super::{
-    Barrier, Content, Interruption, Layout, Level, Node, SequenceNode, Show, StyleChain,
-    StyleEntry, StyleMap, StyleVecBuilder, StyledNode, Target,
-};
-use crate::diag::SourceResult;
-use crate::geom::Numeric;
-use crate::library::layout::{
-    ColbreakNode, FlowChild, FlowNode, HNode, PageNode, PagebreakNode, PlaceNode, VNode,
-};
-use crate::library::structure::{DocNode, ListItem, ListNode, DESC, ENUM, LIST};
-use crate::library::text::{
-    LinebreakNode, ParChild, ParNode, ParbreakNode, SmartQuoteNode, SpaceNode, TextNode,
-};
-use crate::World;
-
-/// Builds a document or a flow node from content.
-pub(super) struct Builder<'a> {
-    /// The core context.
-    world: Tracked<'a, dyn World>,
-    /// Scratch arenas for building.
-    scratch: &'a Scratch<'a>,
-    /// The current document building state.
-    doc: Option<DocBuilder<'a>>,
-    /// The current flow building state.
-    flow: FlowBuilder<'a>,
-    /// The current paragraph building state.
-    par: ParBuilder<'a>,
-    /// The current list building state.
-    list: ListBuilder<'a>,
-}
-
-/// Temporary storage arenas for building.
-#[derive(Default)]
-pub(super) struct Scratch<'a> {
-    /// An arena where intermediate style chains are stored.
-    styles: Arena<StyleChain<'a>>,
-    /// An arena where intermediate content resulting from show rules is stored.
-    templates: Arena<Content>,
-}
-
-impl<'a> Builder<'a> {
-    pub fn new(
-        world: Tracked<'a, dyn World>,
-        scratch: &'a Scratch<'a>,
-        top: bool,
-    ) -> Self {
-        Self {
-            world,
-            scratch,
-            doc: top.then(|| DocBuilder::default()),
-            flow: FlowBuilder::default(),
-            par: ParBuilder::default(),
-            list: ListBuilder::default(),
-        }
-    }
-
-    pub fn into_doc(
-        mut self,
-        styles: StyleChain<'a>,
-    ) -> SourceResult<(DocNode, StyleChain<'a>)> {
-        self.interrupt(Interruption::Page, styles, true)?;
-        let (pages, shared) = self.doc.unwrap().pages.finish();
-        Ok((DocNode(pages), shared))
-    }
-
-    pub fn into_flow(
-        mut self,
-        styles: StyleChain<'a>,
-    ) -> SourceResult<(FlowNode, StyleChain<'a>)> {
-        self.interrupt(Interruption::Par, styles, false)?;
-        let (children, shared) = self.flow.0.finish();
-        Ok((FlowNode(children), shared))
-    }
-
-    pub fn accept(
-        &mut self,
-        content: &'a Content,
-        styles: StyleChain<'a>,
-    ) -> SourceResult<()> {
-        if let Some(node) = content.downcast::<TextNode>() {
-            if let Some(realized) = styles.apply(self.world, Target::Text(&node.0))? {
-                let stored = self.scratch.templates.alloc(realized);
-                return self.accept(stored, styles);
-            }
-        } else if let Some(styled) = content.downcast::<StyledNode>() {
-            return self.styled(styled, styles);
-        } else if let Some(seq) = content.downcast::<SequenceNode>() {
-            return self.sequence(seq, styles);
-        } else if content.has::<dyn Show>() {
-            if self.show(&content, styles)? {
-                return Ok(());
-            }
-        }
-
-        if self.list.accept(content, styles) {
-            return Ok(());
-        }
-
-        self.interrupt(Interruption::List, styles, false)?;
-
-        if content.is::<ListItem>() {
-            self.list.accept(content, styles);
-            return Ok(());
-        }
-
-        if self.par.accept(content, styles) {
-            return Ok(());
-        }
-
-        self.interrupt(Interruption::Par, styles, false)?;
-
-        if self.flow.accept(content, styles) {
-            return Ok(());
-        }
-
-        let keep = content.downcast::<PagebreakNode>().map_or(false, |node| !node.weak);
-        self.interrupt(Interruption::Page, styles, keep)?;
-
-        if let Some(doc) = &mut self.doc {
-            doc.accept(content, styles);
-        }
-
-        // We might want to issue a warning or error for content that wasn't
-        // handled (e.g. a pagebreak in a flow building process). However, we
-        // don't have the spans here at the moment.
-        Ok(())
-    }
-
-    fn show(&mut self, node: &'a Content, styles: StyleChain<'a>) -> SourceResult<bool> {
-        if let Some(mut realized) = styles.apply(self.world, Target::Node(node))? {
-            let mut map = StyleMap::new();
-            let barrier = Barrier::new(node.id());
-            map.push(StyleEntry::Barrier(barrier));
-            map.push(StyleEntry::Barrier(barrier));
-            realized = realized.styled_with_map(map);
-            let stored = self.scratch.templates.alloc(realized);
-            self.accept(stored, styles)?;
-            Ok(true)
-        } else {
-            Ok(false)
-        }
-    }
-
-    fn styled(
-        &mut self,
-        styled: &'a StyledNode,
-        styles: StyleChain<'a>,
-    ) -> SourceResult<()> {
-        let stored = self.scratch.styles.alloc(styles);
-        let styles = styled.map.chain(stored);
-        let intr = styled.map.interruption();
-
-        if let Some(intr) = intr {
-            self.interrupt(intr, styles, false)?;
-        }
-
-        self.accept(&styled.sub, styles)?;
-
-        if let Some(intr) = intr {
-            self.interrupt(intr, styles, true)?;
-        }
-
-        Ok(())
-    }
-
-    fn interrupt(
-        &mut self,
-        intr: Interruption,
-        styles: StyleChain<'a>,
-        keep: bool,
-    ) -> SourceResult<()> {
-        if intr >= Interruption::List && !self.list.is_empty() {
-            mem::take(&mut self.list).finish(self)?;
-        }
-
-        if intr >= Interruption::Par {
-            if !self.par.is_empty() {
-                mem::take(&mut self.par).finish(self);
-            }
-        }
-
-        if intr >= Interruption::Page {
-            if let Some(doc) = &mut self.doc {
-                if !self.flow.is_empty() || (doc.keep_next && keep) {
-                    mem::take(&mut self.flow).finish(doc, styles);
-                }
-                doc.keep_next = !keep;
-            }
-        }
-
-        Ok(())
-    }
-
-    fn sequence(
-        &mut self,
-        seq: &'a SequenceNode,
-        styles: StyleChain<'a>,
-    ) -> SourceResult<()> {
-        for content in &seq.0 {
-            self.accept(content, styles)?;
-        }
-        Ok(())
-    }
-}
-
-/// Accepts pagebreaks and pages.
-struct DocBuilder<'a> {
-    /// The page runs built so far.
-    pages: StyleVecBuilder<'a, PageNode>,
-    /// Whether to keep a following page even if it is empty.
-    keep_next: bool,
-}
-
-impl<'a> DocBuilder<'a> {
-    fn accept(&mut self, content: &'a Content, styles: StyleChain<'a>) {
-        if let Some(pagebreak) = content.downcast::<PagebreakNode>() {
-            self.keep_next = !pagebreak.weak;
-        }
-
-        if let Some(page) = content.downcast::<PageNode>() {
-            self.pages.push(page.clone(), styles);
-            self.keep_next = false;
-        }
-    }
-}
-
-impl Default for DocBuilder<'_> {
-    fn default() -> Self {
-        Self {
-            pages: StyleVecBuilder::new(),
-            keep_next: true,
-        }
-    }
-}
-
-/// Accepts flow content.
-#[derive(Default)]
-struct FlowBuilder<'a>(CollapsingBuilder<'a, FlowChild>);
-
-impl<'a> FlowBuilder<'a> {
-    fn accept(&mut self, content: &'a Content, styles: StyleChain<'a>) -> bool {
-        // Weak flow elements:
-        // Weakness | Element
-        //    0     | weak colbreak
-        //    1     | weak fractional spacing
-        //    2     | weak spacing
-        //    3     | generated weak spacing
-        //    4     | generated weak fractional spacing
-        //    5     | par spacing
-
-        if let Some(_) = content.downcast::<ParbreakNode>() {
-            /* Nothing to do */
-        } else if let Some(colbreak) = content.downcast::<ColbreakNode>() {
-            if colbreak.weak {
-                self.0.weak(FlowChild::Colbreak, styles, 0);
-            } else {
-                self.0.destructive(FlowChild::Colbreak, styles);
-            }
-        } else if let Some(vertical) = content.downcast::<VNode>() {
-            let child = FlowChild::Spacing(vertical.amount);
-            let frac = vertical.amount.is_fractional();
-            if vertical.weak {
-                let weakness = 1 + u8::from(frac) + 2 * u8::from(vertical.generated);
-                self.0.weak(child, styles, weakness);
-            } else if frac {
-                self.0.destructive(child, styles);
-            } else {
-                self.0.ignorant(child, styles);
-            }
-        } else if content.has::<dyn Layout>() {
-            let child = FlowChild::Node(content.clone());
-            if content.is::<PlaceNode>() {
-                self.0.ignorant(child, styles);
-            } else {
-                self.0.supportive(child, styles);
-            }
-        } else {
-            return false;
-        }
-
-        true
-    }
-
-    fn par(&mut self, par: ParNode, styles: StyleChain<'a>, indent: bool) {
-        let amount = if indent && !styles.get(ParNode::SPACING_AND_INDENT) {
-            styles.get(ParNode::LEADING).into()
-        } else {
-            styles.get(ParNode::SPACING).into()
-        };
-
-        self.0.weak(FlowChild::Spacing(amount), styles, 5);
-        self.0.supportive(FlowChild::Node(par.pack()), styles);
-        self.0.weak(FlowChild::Spacing(amount), styles, 5);
-    }
-
-    fn finish(self, doc: &mut DocBuilder<'a>, styles: StyleChain<'a>) {
-        let (flow, shared) = self.0.finish();
-        let styles = if flow.is_empty() { styles } else { shared };
-        let node = PageNode(FlowNode(flow).pack());
-        doc.pages.push(node, styles);
-    }
-
-    fn is_empty(&self) -> bool {
-        self.0.is_empty()
-    }
-}
-
-/// Accepts paragraph content.
-#[derive(Default)]
-struct ParBuilder<'a>(CollapsingBuilder<'a, ParChild>);
-
-impl<'a> ParBuilder<'a> {
-    fn accept(&mut self, content: &'a Content, styles: StyleChain<'a>) -> bool {
-        // Weak par elements:
-        // Weakness | Element
-        //    0     | weak fractional spacing
-        //    1     | weak spacing
-        //    2     | space
-
-        if content.is::<SpaceNode>() {
-            self.0.weak(ParChild::Text(' '.into()), styles, 2);
-        } else if let Some(linebreak) = content.downcast::<LinebreakNode>() {
-            let c = if linebreak.justify { '\u{2028}' } else { '\n' };
-            self.0.destructive(ParChild::Text(c.into()), styles);
-        } else if let Some(horizontal) = content.downcast::<HNode>() {
-            let child = ParChild::Spacing(horizontal.amount);
-            let frac = horizontal.amount.is_fractional();
-            if horizontal.weak {
-                let weakness = u8::from(!frac);
-                self.0.weak(child, styles, weakness);
-            } else if frac {
-                self.0.destructive(child, styles);
-            } else {
-                self.0.ignorant(child, styles);
-            }
-        } else if let Some(quote) = content.downcast::<SmartQuoteNode>() {
-            self.0.supportive(ParChild::Quote { double: quote.double }, styles);
-        } else if let Some(node) = content.downcast::<TextNode>() {
-            self.0.supportive(ParChild::Text(node.0.clone()), styles);
-        } else if let Some(node) = content.to::<dyn Layout>() {
-            if node.level() == Level::Inline {
-                self.0.supportive(ParChild::Node(content.clone()), styles);
-            } else {
-                return false;
-            }
-        } else {
-            return false;
-        }
-
-        true
-    }
-
-    fn finish(self, parent: &mut Builder<'a>) {
-        let (mut children, shared) = self.0.finish();
-        if children.is_empty() {
-            return;
-        }
-
-        // Paragraph indent should only apply if the paragraph starts with
-        // text and follows directly after another paragraph.
-        let indent = shared.get(ParNode::INDENT);
-        if !indent.is_zero()
-            && children
-                .items()
-                .find_map(|child| match child {
-                    ParChild::Spacing(_) => None,
-                    ParChild::Text(_) | ParChild::Quote { .. } => Some(true),
-                    ParChild::Node(_) => Some(false),
-                })
-                .unwrap_or_default()
-            && parent
-                .flow
-                .0
-                .items()
-                .rev()
-                .find_map(|child| match child {
-                    FlowChild::Spacing(_) => None,
-                    FlowChild::Node(node) => Some(node.is::<ParNode>()),
-                    FlowChild::Colbreak => Some(false),
-                })
-                .unwrap_or_default()
-        {
-            children.push_front(ParChild::Spacing(indent.into()));
-        }
-
-        parent.flow.par(ParNode(children), shared, !indent.is_zero());
-    }
-
-    fn is_empty(&self) -> bool {
-        self.0.is_empty()
-    }
-}
-
-/// Accepts list / enum items, spaces, paragraph breaks.
-struct ListBuilder<'a> {
-    /// The list items collected so far.
-    items: StyleVecBuilder<'a, ListItem>,
-    /// Whether the list contains no paragraph breaks.
-    tight: bool,
-    /// Whether the list can be attached.
-    attachable: bool,
-    /// Trailing content for which it is unclear whether it is part of the list.
-    staged: Vec<(&'a Content, StyleChain<'a>)>,
-}
-
-impl<'a> ListBuilder<'a> {
-    fn accept(&mut self, content: &'a Content, styles: StyleChain<'a>) -> bool {
-        if self.items.is_empty() {
-            if content.is::<ParbreakNode>() {
-                self.attachable = false;
-            } else if !content.is::<SpaceNode>() && !content.is::<ListItem>() {
-                self.attachable = true;
-            }
-        }
-
-        if let Some(item) = content.downcast::<ListItem>() {
-            if self
-                .items
-                .items()
-                .next()
-                .map_or(true, |first| item.kind() == first.kind())
-            {
-                self.items.push(item.clone(), styles);
-                self.tight &= self.staged.drain(..).all(|(t, _)| !t.is::<ParbreakNode>());
-            } else {
-                return false;
-            }
-        } else if !self.items.is_empty()
-            && (content.is::<SpaceNode>() || content.is::<ParbreakNode>())
-        {
-            self.staged.push((content, styles));
-        } else {
-            return false;
-        }
-
-        true
-    }
-
-    fn finish(self, parent: &mut Builder<'a>) -> SourceResult<()> {
-        let (items, shared) = self.items.finish();
-        let kind = match items.items().next() {
-            Some(item) => item.kind(),
-            None => return Ok(()),
-        };
-
-        let tight = self.tight;
-        let attached = tight && self.attachable;
-        let content = match kind {
-            LIST => ListNode::<LIST> { tight, attached, items }.pack(),
-            ENUM => ListNode::<ENUM> { tight, attached, items }.pack(),
-            DESC | _ => ListNode::<DESC> { tight, attached, items }.pack(),
-        };
-
-        let stored = parent.scratch.templates.alloc(content);
-        parent.accept(stored, shared)?;
-
-        for (content, styles) in self.staged {
-            parent.accept(content, styles)?;
-        }
-
-        parent.list.attachable = true;
-
-        Ok(())
-    }
-
-    fn is_empty(&self) -> bool {
-        self.items.is_empty()
-    }
-}
-
-impl Default for ListBuilder<'_> {
-    fn default() -> Self {
-        Self {
-            items: StyleVecBuilder::default(),
-            tight: true,
-            attachable: true,
-            staged: vec![],
-        }
-    }
-}
diff --git a/src/model/recipe.rs b/src/model/recipe.rs
deleted file mode 100644
index c687f4fb..00000000
--- a/src/model/recipe.rs
+++ /dev/null
@@ -1,185 +0,0 @@
-use std::fmt::{self, Debug, Formatter};
-use std::hash::Hash;
-
-use comemo::Tracked;
-
-use super::{
-    Args, Capability, Content, Func, Interruption, Node, NodeId, Regex, StyleChain,
-    StyleEntry, Value,
-};
-use crate::diag::SourceResult;
-use crate::library::structure::{DescNode, EnumNode, ListNode};
-use crate::library::text::TextNode;
-use crate::syntax::Spanned;
-use crate::World;
-
-/// A show rule recipe.
-#[derive(Clone, PartialEq, Hash)]
-pub struct Recipe {
-    /// The patterns to customize.
-    pub pattern: Pattern,
-    /// The function that defines the recipe.
-    pub func: Spanned<Func>,
-}
-
-impl Recipe {
-    /// Whether the recipe is applicable to the target.
-    pub fn applicable(&self, target: Target) -> bool {
-        match (&self.pattern, target) {
-            (Pattern::Node(id), Target::Node(node)) => *id == node.id(),
-            (Pattern::Regex(_), Target::Text(_)) => true,
-            _ => false,
-        }
-    }
-
-    /// Try to apply the recipe to the target.
-    pub fn apply(
-        &self,
-        world: Tracked<dyn World>,
-        sel: Selector,
-        target: Target,
-    ) -> SourceResult<Option<Content>> {
-        let content = match (target, &self.pattern) {
-            (Target::Node(node), &Pattern::Node(id)) if node.id() == id => {
-                let node = node.to::<dyn Show>().unwrap().unguard_parts(sel);
-                self.call(world, || Value::Content(node))?
-            }
-
-            (Target::Text(text), Pattern::Regex(regex)) => {
-                let mut result = vec![];
-                let mut cursor = 0;
-
-                for mat in regex.find_iter(text) {
-                    let start = mat.start();
-                    if cursor < start {
-                        result.push(TextNode(text[cursor .. start].into()).pack());
-                    }
-
-                    result.push(self.call(world, || Value::Str(mat.as_str().into()))?);
-                    cursor = mat.end();
-                }
-
-                if result.is_empty() {
-                    return Ok(None);
-                }
-
-                if cursor < text.len() {
-                    result.push(TextNode(text[cursor ..].into()).pack());
-                }
-
-                Content::sequence(result)
-            }
-
-            _ => return Ok(None),
-        };
-
-        Ok(Some(content.styled_with_entry(StyleEntry::Guard(sel))))
-    }
-
-    /// Call the recipe function, with the argument if desired.
-    fn call<F>(&self, world: Tracked<dyn World>, arg: F) -> SourceResult<Content>
-    where
-        F: FnOnce() -> Value,
-    {
-        let args = if self.func.v.argc() == Some(0) {
-            Args::new(self.func.span, [])
-        } else {
-            Args::new(self.func.span, [arg()])
-        };
-
-        Ok(self.func.v.call_detached(world, args)?.display(world))
-    }
-
-    /// What kind of structure the property interrupts.
-    pub fn interruption(&self) -> Option<Interruption> {
-        if let Pattern::Node(id) = self.pattern {
-            if id == NodeId::of::<ListNode>()
-                || id == NodeId::of::<EnumNode>()
-                || id == NodeId::of::<DescNode>()
-            {
-                return Some(Interruption::List);
-            }
-        }
-
-        None
-    }
-}
-
-impl Debug for Recipe {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        write!(
-            f,
-            "Recipe matching {:?} from {:?}",
-            self.pattern, self.func.span
-        )
-    }
-}
-
-/// A show rule pattern that may match a target.
-#[derive(Debug, Clone, PartialEq, Hash)]
-pub enum Pattern {
-    /// Defines the appearence of some node.
-    Node(NodeId),
-    /// Defines text to be replaced.
-    Regex(Regex),
-}
-
-impl Pattern {
-    /// Define a simple text replacement pattern.
-    pub fn text(text: &str) -> Self {
-        Self::Regex(Regex::new(&regex::escape(text)).unwrap())
-    }
-}
-
-/// A target for a show rule recipe.
-#[derive(Debug, Copy, Clone, PartialEq)]
-pub enum Target<'a> {
-    /// A showable node.
-    Node(&'a Content),
-    /// A slice of text.
-    Text(&'a str),
-}
-
-/// Identifies a show rule recipe.
-#[derive(Debug, Copy, Clone, PartialEq, Hash)]
-pub enum Selector {
-    /// The nth recipe from the top of the chain.
-    Nth(usize),
-    /// The base recipe for a kind of node.
-    Base(NodeId),
-}
-
-/// A node that can be realized given some styles.
-pub trait Show: 'static + Sync + Send {
-    /// Unguard nested content against recursive show rules.
-    fn unguard_parts(&self, sel: Selector) -> Content;
-
-    /// Access a field on this node.
-    fn field(&self, name: &str) -> Option<Value>;
-
-    /// The base recipe for this node that is executed if there is no
-    /// user-defined show rule.
-    fn realize(
-        &self,
-        world: Tracked<dyn World>,
-        styles: StyleChain,
-    ) -> SourceResult<Content>;
-
-    /// Finalize this node given the realization of a base or user recipe. Use
-    /// this for effects that should work even in the face of a user-defined
-    /// show rule, for example:
-    /// - Application of general settable properties
-    ///
-    /// Defaults to just the realized content.
-    #[allow(unused_variables)]
-    fn finalize(
-        &self,
-        world: Tracked<dyn World>,
-        styles: StyleChain,
-        realized: Content,
-    ) -> SourceResult<Content> {
-        Ok(realized)
-    }
-}
-
-impl Capability for dyn Show {}
diff --git a/src/model/resolve.rs b/src/model/resolve.rs
deleted file mode 100644
index 1ca4be69..00000000
--- a/src/model/resolve.rs
+++ /dev/null
@@ -1,84 +0,0 @@
-use super::{Smart, StyleChain};
-use crate::geom::{Abs, Axes, Corners, Em, Length, Numeric, Rel, Sides};
-use crate::library::text::TextNode;
-
-/// A property that is resolved with other properties from the style chain.
-pub trait Resolve {
-    /// The type of the resolved output.
-    type Output;
-
-    /// Resolve the value using the style chain.
-    fn resolve(self, styles: StyleChain) -> Self::Output;
-}
-
-impl Resolve for Em {
-    type Output = Abs;
-
-    fn resolve(self, styles: StyleChain) -> Self::Output {
-        if self.is_zero() {
-            Abs::zero()
-        } else {
-            self.at(styles.get(TextNode::SIZE))
-        }
-    }
-}
-
-impl Resolve for Length {
-    type Output = Abs;
-
-    fn resolve(self, styles: StyleChain) -> Self::Output {
-        self.abs + self.em.resolve(styles)
-    }
-}
-
-impl<T: Resolve> Resolve for Option<T> {
-    type Output = Option<T::Output>;
-
-    fn resolve(self, styles: StyleChain) -> Self::Output {
-        self.map(|v| v.resolve(styles))
-    }
-}
-
-impl<T: Resolve> Resolve for Smart<T> {
-    type Output = Smart<T::Output>;
-
-    fn resolve(self, styles: StyleChain) -> Self::Output {
-        self.map(|v| v.resolve(styles))
-    }
-}
-
-impl<T: Resolve> Resolve for Axes<T> {
-    type Output = Axes<T::Output>;
-
-    fn resolve(self, styles: StyleChain) -> Self::Output {
-        self.map(|v| v.resolve(styles))
-    }
-}
-
-impl<T: Resolve> Resolve for Sides<T> {
-    type Output = Sides<T::Output>;
-
-    fn resolve(self, styles: StyleChain) -> Self::Output {
-        self.map(|v| v.resolve(styles))
-    }
-}
-
-impl<T: Resolve> Resolve for Corners<T> {
-    type Output = Corners<T::Output>;
-
-    fn resolve(self, styles: StyleChain) -> Self::Output {
-        self.map(|v| v.resolve(styles))
-    }
-}
-
-impl<T> Resolve for Rel<T>
-where
-    T: Resolve + Numeric,
-    <T as Resolve>::Output: Numeric,
-{
-    type Output = Rel<<T as Resolve>::Output>;
-
-    fn resolve(self, styles: StyleChain) -> Self::Output {
-        self.map(|abs| abs.resolve(styles))
-    }
-}
diff --git a/src/model/str.rs b/src/model/str.rs
index 62b37845..843da9a8 100644
--- a/src/model/str.rs
+++ b/src/model/str.rs
@@ -5,8 +5,9 @@ use std::ops::{Add, AddAssign, Deref};
 
 use unicode_segmentation::UnicodeSegmentation;
 
-use super::{Array, Dict, RawAlign, Value};
+use super::{Array, Dict, Value};
 use crate::diag::StrResult;
+use crate::library::RawAlign;
 use crate::util::EcoString;
 
 /// Create a new [`Str`] from a format string.
diff --git a/src/model/styles.rs b/src/model/styles.rs
index d160a4a6..c58a1beb 100644
--- a/src/model/styles.rs
+++ b/src/model/styles.rs
@@ -1,12 +1,20 @@
+use std::any::Any;
 use std::fmt::{self, Debug, Formatter};
 use std::hash::Hash;
 use std::iter;
 use std::marker::PhantomData;
+use std::sync::Arc;
 
-use comemo::Tracked;
+use comemo::{Prehashed, Tracked};
 
-use super::{Barrier, Content, Key, Property, Recipe, Selector, Show, Target};
+use super::{capability, Args, Content, Func, Node, NodeId, Regex, Smart, Value};
 use crate::diag::SourceResult;
+use crate::geom::{Abs, Axes, Corners, Em, Length, Numeric, Rel, Sides};
+use crate::library::layout::PageNode;
+use crate::library::structure::{DescNode, EnumNode, ListNode};
+use crate::library::text::{ParNode, TextNode};
+use crate::syntax::Spanned;
+use crate::util::ReadableTypeId;
 use crate::World;
 
 /// A map of style properties.
@@ -618,3 +626,516 @@ impl<'a, T> Default for StyleVecBuilder<'a, T> {
         Self::new()
     }
 }
+
+/// A style property originating from a set rule or constructor.
+#[derive(Clone, Hash)]
+pub struct Property {
+    /// The id of the property's [key](Key).
+    key: KeyId,
+    /// The id of the node the property belongs to.
+    node: NodeId,
+    /// Whether the property should only affect the first node down the
+    /// hierarchy. Used by constructors.
+    scoped: bool,
+    /// The property's value.
+    value: Arc<Prehashed<dyn Bounds>>,
+    /// The name of the property.
+    #[cfg(debug_assertions)]
+    name: &'static str,
+}
+
+impl Property {
+    /// Create a new property from a key-value pair.
+    pub fn new<'a, K: Key<'a>>(_: K, value: K::Value) -> Self {
+        Self {
+            key: KeyId::of::<K>(),
+            node: K::node(),
+            value: Arc::new(Prehashed::new(value)),
+            scoped: false,
+            #[cfg(debug_assertions)]
+            name: K::NAME,
+        }
+    }
+
+    /// Whether this property has the given key.
+    pub fn is<'a, K: Key<'a>>(&self) -> bool {
+        self.key == KeyId::of::<K>()
+    }
+
+    /// Whether this property belongs to the node `T`.
+    pub fn is_of<T: 'static>(&self) -> bool {
+        self.node == NodeId::of::<T>()
+    }
+
+    /// Access the property's value if it is of the given key.
+    pub fn downcast<'a, K: Key<'a>>(&'a self) -> Option<&'a K::Value> {
+        if self.key == KeyId::of::<K>() {
+            (**self.value).as_any().downcast_ref()
+        } else {
+            None
+        }
+    }
+
+    /// The node this property is for.
+    pub fn node(&self) -> NodeId {
+        self.node
+    }
+
+    /// Whether the property is scoped.
+    pub fn scoped(&self) -> bool {
+        self.scoped
+    }
+
+    /// Make the property scoped.
+    pub fn make_scoped(&mut self) {
+        self.scoped = true;
+    }
+
+    /// What kind of structure the property interrupts.
+    pub fn interruption(&self) -> Option<Interruption> {
+        if self.is_of::<PageNode>() {
+            Some(Interruption::Page)
+        } else if self.is_of::<ParNode>() {
+            Some(Interruption::Par)
+        } else if self.is_of::<ListNode>()
+            || self.is_of::<EnumNode>()
+            || self.is_of::<DescNode>()
+        {
+            Some(Interruption::List)
+        } else {
+            None
+        }
+    }
+}
+
+impl Debug for Property {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        #[cfg(debug_assertions)]
+        write!(f, "{} = ", self.name)?;
+        write!(f, "{:?}", self.value)?;
+        if self.scoped {
+            write!(f, " [scoped]")?;
+        }
+        Ok(())
+    }
+}
+
+impl PartialEq for Property {
+    fn eq(&self, other: &Self) -> bool {
+        self.key == other.key
+            && self.value.eq(&other.value)
+            && self.scoped == other.scoped
+    }
+}
+
+trait Bounds: Debug + Sync + Send + 'static {
+    fn as_any(&self) -> &dyn Any;
+}
+
+impl<T> Bounds for T
+where
+    T: Debug + Sync + Send + 'static,
+{
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+}
+
+/// A style property key.
+///
+/// This trait is not intended to be implemented manually, but rather through
+/// the `#[node]` proc-macro.
+pub trait Key<'a>: Copy + 'static {
+    /// The unfolded type which this property is stored as in a style map.
+    type Value: Debug + Clone + Hash + Sync + Send + 'static;
+
+    /// The folded type of value that is returned when reading this property
+    /// from a style chain.
+    type Output;
+
+    /// The name of the property, used for debug printing.
+    const NAME: &'static str;
+
+    /// The id of the node the key belongs to.
+    fn node() -> NodeId;
+
+    /// Compute an output value from a sequence of values belonging to this key,
+    /// folding if necessary.
+    fn get(
+        chain: StyleChain<'a>,
+        values: impl Iterator<Item = &'a Self::Value>,
+    ) -> Self::Output;
+}
+
+/// A unique identifier for a property key.
+#[derive(Copy, Clone, Eq, PartialEq, Hash)]
+struct KeyId(ReadableTypeId);
+
+impl KeyId {
+    /// The id of the given key.
+    pub fn of<'a, T: Key<'a>>() -> Self {
+        Self(ReadableTypeId::of::<T>())
+    }
+}
+
+impl Debug for KeyId {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+/// A scoped property barrier.
+///
+/// Barriers interact with [scoped](super::StyleMap::scoped) styles: A scoped
+/// style can still be read through a single barrier (the one of the node it
+/// _should_ apply to), but a second barrier will make it invisible.
+#[derive(Copy, Clone, Eq, PartialEq, Hash)]
+pub struct Barrier(NodeId);
+
+impl Barrier {
+    /// Create a new barrier for the given node.
+    pub fn new(node: NodeId) -> Self {
+        Self(node)
+    }
+
+    /// Whether this barrier is for the node `T`.
+    pub fn is_for(&self, node: NodeId) -> bool {
+        self.0 == node
+    }
+}
+
+impl Debug for Barrier {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "Barrier for {:?}", self.0)
+    }
+}
+
+/// A property that is resolved with other properties from the style chain.
+pub trait Resolve {
+    /// The type of the resolved output.
+    type Output;
+
+    /// Resolve the value using the style chain.
+    fn resolve(self, styles: StyleChain) -> Self::Output;
+}
+
+impl Resolve for Em {
+    type Output = Abs;
+
+    fn resolve(self, styles: StyleChain) -> Self::Output {
+        if self.is_zero() {
+            Abs::zero()
+        } else {
+            self.at(styles.get(TextNode::SIZE))
+        }
+    }
+}
+
+impl Resolve for Length {
+    type Output = Abs;
+
+    fn resolve(self, styles: StyleChain) -> Self::Output {
+        self.abs + self.em.resolve(styles)
+    }
+}
+
+impl<T: Resolve> Resolve for Option<T> {
+    type Output = Option<T::Output>;
+
+    fn resolve(self, styles: StyleChain) -> Self::Output {
+        self.map(|v| v.resolve(styles))
+    }
+}
+
+impl<T: Resolve> Resolve for Smart<T> {
+    type Output = Smart<T::Output>;
+
+    fn resolve(self, styles: StyleChain) -> Self::Output {
+        self.map(|v| v.resolve(styles))
+    }
+}
+
+impl<T: Resolve> Resolve for Axes<T> {
+    type Output = Axes<T::Output>;
+
+    fn resolve(self, styles: StyleChain) -> Self::Output {
+        self.map(|v| v.resolve(styles))
+    }
+}
+
+impl<T: Resolve> Resolve for Sides<T> {
+    type Output = Sides<T::Output>;
+
+    fn resolve(self, styles: StyleChain) -> Self::Output {
+        self.map(|v| v.resolve(styles))
+    }
+}
+
+impl<T: Resolve> Resolve for Corners<T> {
+    type Output = Corners<T::Output>;
+
+    fn resolve(self, styles: StyleChain) -> Self::Output {
+        self.map(|v| v.resolve(styles))
+    }
+}
+
+impl<T> Resolve for Rel<T>
+where
+    T: Resolve + Numeric,
+    <T as Resolve>::Output: Numeric,
+{
+    type Output = Rel<<T as Resolve>::Output>;
+
+    fn resolve(self, styles: StyleChain) -> Self::Output {
+        self.map(|abs| abs.resolve(styles))
+    }
+}
+
+/// A property that is folded to determine its final value.
+pub trait Fold {
+    /// The type of the folded output.
+    type Output;
+
+    /// Fold this inner value with an outer folded value.
+    fn fold(self, outer: Self::Output) -> Self::Output;
+}
+
+impl<T> Fold for Option<T>
+where
+    T: Fold,
+    T::Output: Default,
+{
+    type Output = Option<T::Output>;
+
+    fn fold(self, outer: Self::Output) -> Self::Output {
+        self.map(|inner| inner.fold(outer.unwrap_or_default()))
+    }
+}
+
+impl<T> Fold for Smart<T>
+where
+    T: Fold,
+    T::Output: Default,
+{
+    type Output = Smart<T::Output>;
+
+    fn fold(self, outer: Self::Output) -> Self::Output {
+        self.map(|inner| inner.fold(outer.unwrap_or_default()))
+    }
+}
+
+impl<T> Fold for Sides<T>
+where
+    T: Fold,
+{
+    type Output = Sides<T::Output>;
+
+    fn fold(self, outer: Self::Output) -> Self::Output {
+        self.zip(outer, |inner, outer| inner.fold(outer))
+    }
+}
+
+impl Fold for Sides<Option<Rel<Abs>>> {
+    type Output = Sides<Rel<Abs>>;
+
+    fn fold(self, outer: Self::Output) -> Self::Output {
+        self.zip(outer, |inner, outer| inner.unwrap_or(outer))
+    }
+}
+
+impl Fold for Sides<Option<Smart<Rel<Length>>>> {
+    type Output = Sides<Smart<Rel<Length>>>;
+
+    fn fold(self, outer: Self::Output) -> Self::Output {
+        self.zip(outer, |inner, outer| inner.unwrap_or(outer))
+    }
+}
+
+impl<T> Fold for Corners<T>
+where
+    T: Fold,
+{
+    type Output = Corners<T::Output>;
+
+    fn fold(self, outer: Self::Output) -> Self::Output {
+        self.zip(outer, |inner, outer| inner.fold(outer))
+    }
+}
+
+impl Fold for Corners<Option<Rel<Abs>>> {
+    type Output = Corners<Rel<Abs>>;
+
+    fn fold(self, outer: Self::Output) -> Self::Output {
+        self.zip(outer, |inner, outer| inner.unwrap_or(outer))
+    }
+}
+
+/// A show rule recipe.
+#[derive(Clone, PartialEq, Hash)]
+pub struct Recipe {
+    /// The patterns to customize.
+    pub pattern: Pattern,
+    /// The function that defines the recipe.
+    pub func: Spanned<Func>,
+}
+
+impl Recipe {
+    /// Whether the recipe is applicable to the target.
+    pub fn applicable(&self, target: Target) -> bool {
+        match (&self.pattern, target) {
+            (Pattern::Node(id), Target::Node(node)) => *id == node.id(),
+            (Pattern::Regex(_), Target::Text(_)) => true,
+            _ => false,
+        }
+    }
+
+    /// Try to apply the recipe to the target.
+    pub fn apply(
+        &self,
+        world: Tracked<dyn World>,
+        sel: Selector,
+        target: Target,
+    ) -> SourceResult<Option<Content>> {
+        let content = match (target, &self.pattern) {
+            (Target::Node(node), &Pattern::Node(id)) if node.id() == id => {
+                let node = node.to::<dyn Show>().unwrap().unguard_parts(sel);
+                self.call(world, || Value::Content(node))?
+            }
+
+            (Target::Text(text), Pattern::Regex(regex)) => {
+                let mut result = vec![];
+                let mut cursor = 0;
+
+                for mat in regex.find_iter(text) {
+                    let start = mat.start();
+                    if cursor < start {
+                        result.push(TextNode(text[cursor .. start].into()).pack());
+                    }
+
+                    result.push(self.call(world, || Value::Str(mat.as_str().into()))?);
+                    cursor = mat.end();
+                }
+
+                if result.is_empty() {
+                    return Ok(None);
+                }
+
+                if cursor < text.len() {
+                    result.push(TextNode(text[cursor ..].into()).pack());
+                }
+
+                Content::sequence(result)
+            }
+
+            _ => return Ok(None),
+        };
+
+        Ok(Some(content.styled_with_entry(StyleEntry::Guard(sel))))
+    }
+
+    /// Call the recipe function, with the argument if desired.
+    fn call<F>(&self, world: Tracked<dyn World>, arg: F) -> SourceResult<Content>
+    where
+        F: FnOnce() -> Value,
+    {
+        let args = if self.func.v.argc() == Some(0) {
+            Args::new(self.func.span, [])
+        } else {
+            Args::new(self.func.span, [arg()])
+        };
+
+        Ok(self.func.v.call_detached(world, args)?.display(world))
+    }
+
+    /// What kind of structure the property interrupts.
+    pub fn interruption(&self) -> Option<Interruption> {
+        if let Pattern::Node(id) = self.pattern {
+            if id == NodeId::of::<ListNode>()
+                || id == NodeId::of::<EnumNode>()
+                || id == NodeId::of::<DescNode>()
+            {
+                return Some(Interruption::List);
+            }
+        }
+
+        None
+    }
+}
+
+impl Debug for Recipe {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(
+            f,
+            "Recipe matching {:?} from {:?}",
+            self.pattern, self.func.span
+        )
+    }
+}
+
+/// A show rule pattern that may match a target.
+#[derive(Debug, Clone, PartialEq, Hash)]
+pub enum Pattern {
+    /// Defines the appearence of some node.
+    Node(NodeId),
+    /// Defines text to be replaced.
+    Regex(Regex),
+}
+
+impl Pattern {
+    /// Define a simple text replacement pattern.
+    pub fn text(text: &str) -> Self {
+        Self::Regex(Regex::new(&regex::escape(text)).unwrap())
+    }
+}
+
+/// A target for a show rule recipe.
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub enum Target<'a> {
+    /// A showable node.
+    Node(&'a Content),
+    /// A slice of text.
+    Text(&'a str),
+}
+
+/// Identifies a show rule recipe.
+#[derive(Debug, Copy, Clone, PartialEq, Hash)]
+pub enum Selector {
+    /// The nth recipe from the top of the chain.
+    Nth(usize),
+    /// The base recipe for a kind of node.
+    Base(NodeId),
+}
+
+/// A node that can be realized given some styles.
+#[capability]
+pub trait Show: 'static + Sync + Send {
+    /// Unguard nested content against recursive show rules.
+    fn unguard_parts(&self, sel: Selector) -> Content;
+
+    /// Access a field on this node.
+    fn field(&self, name: &str) -> Option<Value>;
+
+    /// The base recipe for this node that is executed if there is no
+    /// user-defined show rule.
+    fn realize(
+        &self,
+        world: Tracked<dyn World>,
+        styles: StyleChain,
+    ) -> SourceResult<Content>;
+
+    /// Finalize this node given the realization of a base or user recipe. Use
+    /// this for effects that should work even in the face of a user-defined
+    /// show rule, for example:
+    /// - Application of general settable properties
+    ///
+    /// Defaults to just the realized content.
+    #[allow(unused_variables)]
+    fn finalize(
+        &self,
+        world: Tracked<dyn World>,
+        styles: StyleChain,
+        realized: Content,
+    ) -> SourceResult<Content> {
+        Ok(realized)
+    }
+}
diff --git a/src/model/value.rs b/src/model/value.rs
index 4741401c..d68f42a0 100644
--- a/src/model/value.rs
+++ b/src/model/value.rs
@@ -307,7 +307,7 @@ where
     }
 
     fn hash128(&self) -> u128 {
-        // Also hash the TypeId since nodes with different types but
+        // Also hash the TypeId since values with different types but
         // equal data should be different.
         let mut state = SipHasher::new();
         self.type_id().hash(&mut state);