diff --git a/benches/oneshot.rs b/benches/oneshot.rs
index bb385688f..6bfb923b4 100644
--- a/benches/oneshot.rs
+++ b/benches/oneshot.rs
@@ -60,7 +60,7 @@ fn bench_eval(iai: &mut Iai) {
 fn bench_to_tree(iai: &mut Iai) {
     let (mut ctx, id) = context();
     let module = ctx.evaluate(id).unwrap();
-    iai.run(|| module.template.to_pages(ctx.style()));
+    iai.run(|| module.template.to_document(ctx.style()));
 }
 
 fn bench_layout(iai: &mut Iai) {
diff --git a/src/eval/template.rs b/src/eval/template.rs
index 8fec398de..82a069f93 100644
--- a/src/eval/template.rs
+++ b/src/eval/template.rs
@@ -7,9 +7,10 @@ use std::rc::Rc;
 
 use crate::diag::StrResult;
 use crate::geom::{Align, Dir, GenAxis, Length, Linear, Sides, Size};
-use crate::layout::{BlockLevel, BlockNode, InlineLevel, InlineNode, PageNode};
+use crate::layout::{Layout, PackedNode};
 use crate::library::{
-    Decoration, FlowChild, FlowNode, PadNode, ParChild, ParNode, Spacing,
+    Decoration, DocumentNode, FlowChild, FlowNode, PadNode, PageNode, ParChild, ParNode,
+    Spacing,
 };
 use crate::style::Style;
 use crate::util::EcoString;
@@ -36,9 +37,9 @@ enum TemplateNode {
     /// A decorated template.
     Decorated(Decoration, Template),
     /// An inline node builder.
-    Inline(Rc<dyn Fn(&Style) -> InlineNode>),
-    /// An block node builder.
-    Block(Rc<dyn Fn(&Style) -> BlockNode>),
+    Inline(Rc<dyn Fn(&Style) -> PackedNode>),
+    /// A block node builder.
+    Block(Rc<dyn Fn(&Style) -> PackedNode>),
     /// Save the current style.
     Save,
     /// Restore the last saved style.
@@ -57,7 +58,7 @@ impl Template {
     pub fn from_inline<F, T>(f: F) -> Self
     where
         F: Fn(&Style) -> T + 'static,
-        T: InlineLevel + Hash + 'static,
+        T: Layout + Hash + 'static,
     {
         let node = TemplateNode::Inline(Rc::new(move |s| f(s).pack()));
         Self(Rc::new(vec![node]))
@@ -67,7 +68,7 @@ impl Template {
     pub fn from_block<F, T>(f: F) -> Self
     where
         F: Fn(&Style) -> T + 'static,
-        T: BlockLevel + Hash + 'static,
+        T: Layout + Hash + 'static,
     {
         let node = TemplateNode::Block(Rc::new(move |s| f(s).pack()));
         Self(Rc::new(vec![node]))
@@ -158,10 +159,10 @@ impl Template {
 
     /// Build the layout tree resulting from instantiating the template with the
     /// given style.
-    pub fn to_pages(&self, style: &Style) -> Vec<PageNode> {
+    pub fn to_document(&self, style: &Style) -> DocumentNode {
         let mut builder = Builder::new(style, true);
         builder.template(self);
-        builder.build_pages()
+        builder.build_document()
     }
 
     /// Repeat this template `n` times.
@@ -327,13 +328,13 @@ impl Builder {
     }
 
     /// Push an inline node into the active paragraph.
-    fn inline(&mut self, node: impl Into<InlineNode>) {
+    fn inline(&mut self, node: impl Into<PackedNode>) {
         let align = self.style.aligns.inline;
         self.flow.par.push(ParChild::Node(node.into(), align));
     }
 
     /// Push a block node into the active flow, finishing the active paragraph.
-    fn block(&mut self, node: impl Into<BlockNode>) {
+    fn block(&mut self, node: impl Into<PackedNode>) {
         self.parbreak();
         self.flow.push(FlowChild::Node(node.into(), self.style.aligns.block));
         self.parbreak();
@@ -359,10 +360,10 @@ impl Builder {
     }
 
     /// Finish building and return the created layout tree.
-    fn build_pages(mut self) -> Vec<PageNode> {
+    fn build_document(mut self) -> DocumentNode {
         assert!(self.page.is_some());
         self.pagebreak(true, false);
-        self.finished
+        DocumentNode { pages: self.finished }
     }
 
     /// Construct a text node with the given text and settings from the current
diff --git a/src/eval/walk.rs b/src/eval/walk.rs
index 7b3fb7a4d..134f10c70 100644
--- a/src/eval/walk.rs
+++ b/src/eval/walk.rs
@@ -3,7 +3,7 @@ use std::rc::Rc;
 use super::{Eval, EvalContext, Template, Value};
 use crate::diag::TypResult;
 use crate::geom::Spec;
-use crate::layout::BlockLevel;
+use crate::layout::Layout;
 use crate::library::{GridNode, ParChild, ParNode, TrackSizing};
 use crate::syntax::ast::*;
 use crate::util::{BoolExt, EcoString};
diff --git a/src/export/pdf.rs b/src/export/pdf.rs
index d517aadfc..24944246d 100644
--- a/src/export/pdf.rs
+++ b/src/export/pdf.rs
@@ -19,13 +19,13 @@ use crate::geom::{self, Color, Em, Length, Paint, Size};
 use crate::image::{Image, ImageId, ImageStore};
 use crate::Context;
 
-/// Export a collection of frames into a PDF document.
+/// Export a collection of frames into a PDF file.
 ///
 /// This creates one page per frame. In addition to the frames, you need to pass
 /// in the context used during compilation such that things like fonts and
 /// images can be included in the PDF.
 ///
-/// Returns the raw bytes making up the PDF document.
+/// Returns the raw bytes making up the PDF file.
 pub fn pdf(ctx: &Context, frames: &[Rc<Frame>]) -> Vec<u8> {
     PdfExporter::new(ctx, frames).write()
 }
diff --git a/src/layout/constraints.rs b/src/layout/constraints.rs
index fdcda276d..36cfa582c 100644
--- a/src/layout/constraints.rs
+++ b/src/layout/constraints.rs
@@ -1,7 +1,7 @@
 use std::rc::Rc;
 
 use crate::frame::Frame;
-use crate::geom::{Length, Size, Spec};
+use crate::geom::{Length, Linear, Size, Spec};
 
 /// Constrain a frame with constraints.
 pub trait Constrain {
@@ -68,6 +68,18 @@ impl Constraints {
             && verify(self.exact, current, Length::approx_eq)
             && verify(self.base, base, Length::approx_eq)
     }
+
+    /// Set the appropriate base constraints for linear width and height sizing.
+    pub fn set_base_if_linear(&mut self, base: Size, sizing: Spec<Option<Linear>>) {
+        // The full sizes need to be equal if there is a relative component in
+        // the sizes.
+        if sizing.x.map_or(false, |l| l.is_relative()) {
+            self.base.x = Some(base.w);
+        }
+        if sizing.y.map_or(false, |l| l.is_relative()) {
+            self.base.y = Some(base.h);
+        }
+    }
 }
 
 /// Verify a single constraint.
diff --git a/src/layout/levels.rs b/src/layout/levels.rs
deleted file mode 100644
index a6b8d0503..000000000
--- a/src/layout/levels.rs
+++ /dev/null
@@ -1,199 +0,0 @@
-use std::fmt::{self, Debug, Formatter};
-use std::hash::{Hash, Hasher};
-use std::rc::Rc;
-
-use super::*;
-use crate::geom::{Length, Size};
-
-/// Page-level nodes directly produce frames representing pages.
-///
-/// Such nodes create their own regions instead of being supplied with them from
-/// some parent.
-pub trait PageLevel: Debug {
-    /// Layout the node, producing one frame per page.
-    fn layout(&self, ctx: &mut LayoutContext) -> Vec<Rc<Frame>>;
-}
-
-/// Layouts its children onto one or multiple pages.
-#[derive(Debug)]
-pub struct PageNode {
-    /// The size of the page.
-    pub size: Size,
-    /// The node that produces the actual pages.
-    pub child: BlockNode,
-}
-
-impl PageLevel for PageNode {
-    fn layout(&self, ctx: &mut LayoutContext) -> Vec<Rc<Frame>> {
-        // When one of the lengths is infinite the page fits its content along
-        // that axis.
-        let expand = self.size.to_spec().map(Length::is_finite);
-        let regions = Regions::repeat(self.size, self.size, expand);
-        self.child.layout(ctx, &regions).into_iter().map(|c| c.item).collect()
-    }
-}
-
-impl<T> PageLevel for T
-where
-    T: AsRef<[PageNode]> + Debug + ?Sized,
-{
-    fn layout(&self, ctx: &mut LayoutContext) -> Vec<Rc<Frame>> {
-        self.as_ref().iter().flat_map(|node| node.layout(ctx)).collect()
-    }
-}
-
-/// Block-level nodes can be layouted into a sequence of regions.
-///
-/// They return one frame per used region alongside constraints that define
-/// whether the result is reusable in other regions.
-pub trait BlockLevel: Debug {
-    /// Layout the node into the given regions, producing constrained frames.
-    fn layout(
-        &self,
-        ctx: &mut LayoutContext,
-        regions: &Regions,
-    ) -> Vec<Constrained<Rc<Frame>>>;
-
-    /// Convert to a packed block-level node.
-    fn pack(self) -> BlockNode
-    where
-        Self: Sized + Hash + 'static,
-    {
-        BlockNode {
-            #[cfg(feature = "layout-cache")]
-            hash: hash_node(&self),
-            node: Rc::new(self),
-        }
-    }
-}
-
-/// A packed [block-level](BlockLevel) layouting node with precomputed hash.
-#[derive(Clone)]
-pub struct BlockNode {
-    node: Rc<dyn BlockLevel>,
-    #[cfg(feature = "layout-cache")]
-    hash: u64,
-}
-
-impl BlockLevel for BlockNode {
-    fn layout(
-        &self,
-        ctx: &mut LayoutContext,
-        regions: &Regions,
-    ) -> Vec<Constrained<Rc<Frame>>> {
-        #[cfg(not(feature = "layout-cache"))]
-        return self.node.layout(ctx, regions);
-
-        #[cfg(feature = "layout-cache")]
-        ctx.layouts.get(self.hash, regions).unwrap_or_else(|| {
-            ctx.level += 1;
-            let frames = self.node.layout(ctx, regions);
-            ctx.level -= 1;
-
-            let entry = FramesEntry::new(frames.clone(), ctx.level);
-
-            #[cfg(debug_assertions)]
-            if !entry.check(regions) {
-                eprintln!("node: {:#?}", self.node);
-                eprintln!("regions: {:#?}", regions);
-                eprintln!(
-                    "constraints: {:#?}",
-                    frames.iter().map(|c| c.cts).collect::<Vec<_>>()
-                );
-                panic!("constraints did not match regions they were created for");
-            }
-
-            ctx.layouts.insert(self.hash, entry);
-            frames
-        })
-    }
-
-    fn pack(self) -> BlockNode
-    where
-        Self: Sized + Hash + 'static,
-    {
-        self
-    }
-}
-
-impl Hash for BlockNode {
-    fn hash<H: Hasher>(&self, _state: &mut H) {
-        #[cfg(feature = "layout-cache")]
-        _state.write_u64(self.hash);
-        #[cfg(not(feature = "layout-cache"))]
-        unimplemented!()
-    }
-}
-
-impl Debug for BlockNode {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        self.node.fmt(f)
-    }
-}
-
-/// Inline-level nodes are layouted as part of paragraph layout.
-///
-/// They only know the width and not the height of the paragraph's region and
-/// return only a single frame.
-pub trait InlineLevel: Debug {
-    /// Layout the node into a frame.
-    fn layout(&self, ctx: &mut LayoutContext, space: Length, base: Size) -> Frame;
-
-    /// Convert to a packed inline-level node.
-    fn pack(self) -> InlineNode
-    where
-        Self: Sized + Hash + 'static,
-    {
-        InlineNode {
-            #[cfg(feature = "layout-cache")]
-            hash: hash_node(&self),
-            node: Rc::new(self),
-        }
-    }
-}
-
-/// A packed [inline-level](InlineLevel) layouting node with precomputed hash.
-#[derive(Clone)]
-pub struct InlineNode {
-    node: Rc<dyn InlineLevel>,
-    #[cfg(feature = "layout-cache")]
-    hash: u64,
-}
-
-impl InlineLevel for InlineNode {
-    fn layout(&self, ctx: &mut LayoutContext, space: Length, base: Size) -> Frame {
-        self.node.layout(ctx, space, base)
-    }
-
-    fn pack(self) -> InlineNode
-    where
-        Self: Sized + Hash + 'static,
-    {
-        self
-    }
-}
-
-impl Hash for InlineNode {
-    fn hash<H: Hasher>(&self, _state: &mut H) {
-        #[cfg(feature = "layout-cache")]
-        _state.write_u64(self.hash);
-        #[cfg(not(feature = "layout-cache"))]
-        unimplemented!()
-    }
-}
-
-impl Debug for InlineNode {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        self.node.fmt(f)
-    }
-}
-
-/// Hash a node alongside its type id.
-#[cfg(feature = "layout-cache")]
-fn hash_node(node: &(impl Hash + 'static)) -> u64 {
-    use std::any::Any;
-    let mut state = fxhash::FxHasher64::default();
-    node.type_id().hash(&mut state);
-    node.hash(&mut state);
-    state.finish()
-}
diff --git a/src/layout/mod.rs b/src/layout/mod.rs
index 49ceccf63..7d2837de2 100644
--- a/src/layout/mod.rs
+++ b/src/layout/mod.rs
@@ -1,29 +1,27 @@
-//! Layouting.
+//! Layouting infrastructure.
 
 mod constraints;
 #[cfg(feature = "layout-cache")]
 mod incremental;
-mod levels;
 mod regions;
 
 pub use constraints::*;
 #[cfg(feature = "layout-cache")]
 pub use incremental::*;
-pub use levels::*;
 pub use regions::*;
 
+use std::fmt::{self, Debug, Formatter};
+use std::hash::{Hash, Hasher};
 use std::rc::Rc;
 
 use crate::font::FontStore;
 use crate::frame::Frame;
 use crate::image::ImageStore;
+use crate::library::DocumentNode;
 use crate::Context;
 
-/// Layout a page-level node into a collection of frames.
-pub fn layout<T>(ctx: &mut Context, node: &T) -> Vec<Rc<Frame>>
-where
-    T: PageLevel + ?Sized,
-{
+/// Layout a document node into a collection of frames.
+pub fn layout(ctx: &mut Context, node: &DocumentNode) -> Vec<Rc<Frame>> {
     let mut ctx = LayoutContext::new(ctx);
     node.layout(&mut ctx)
 }
@@ -55,3 +53,98 @@ impl<'a> LayoutContext<'a> {
         }
     }
 }
+
+/// A node that can be layouted into a sequence of regions.
+///
+/// Layout return one frame per used region alongside constraints that define
+/// whether the result is reusable in other regions.
+pub trait Layout: Debug {
+    /// Layout the node into the given regions, producing constrained frames.
+    fn layout(
+        &self,
+        ctx: &mut LayoutContext,
+        regions: &Regions,
+    ) -> Vec<Constrained<Rc<Frame>>>;
+
+    /// Convert to a packed node.
+    fn pack(self) -> PackedNode
+    where
+        Self: Sized + Hash + 'static,
+    {
+        PackedNode {
+            #[cfg(feature = "layout-cache")]
+            hash: {
+                use std::any::Any;
+                let mut state = fxhash::FxHasher64::default();
+                self.type_id().hash(&mut state);
+                self.hash(&mut state);
+                state.finish()
+            },
+            node: Rc::new(self),
+        }
+    }
+}
+
+/// A packed layouting node with precomputed hash.
+#[derive(Clone)]
+pub struct PackedNode {
+    node: Rc<dyn Layout>,
+    #[cfg(feature = "layout-cache")]
+    hash: u64,
+}
+
+impl Layout for PackedNode {
+    fn layout(
+        &self,
+        ctx: &mut LayoutContext,
+        regions: &Regions,
+    ) -> Vec<Constrained<Rc<Frame>>> {
+        #[cfg(not(feature = "layout-cache"))]
+        return self.node.layout(ctx, regions);
+
+        #[cfg(feature = "layout-cache")]
+        ctx.layouts.get(self.hash, regions).unwrap_or_else(|| {
+            ctx.level += 1;
+            let frames = self.node.layout(ctx, regions);
+            ctx.level -= 1;
+
+            let entry = FramesEntry::new(frames.clone(), ctx.level);
+
+            #[cfg(debug_assertions)]
+            if !entry.check(regions) {
+                eprintln!("node: {:#?}", self.node);
+                eprintln!("regions: {:#?}", regions);
+                eprintln!(
+                    "constraints: {:#?}",
+                    frames.iter().map(|c| c.cts).collect::<Vec<_>>()
+                );
+                panic!("constraints did not match regions they were created for");
+            }
+
+            ctx.layouts.insert(self.hash, entry);
+            frames
+        })
+    }
+
+    fn pack(self) -> PackedNode
+    where
+        Self: Sized + Hash + 'static,
+    {
+        self
+    }
+}
+
+impl Hash for PackedNode {
+    fn hash<H: Hasher>(&self, _state: &mut H) {
+        #[cfg(feature = "layout-cache")]
+        _state.write_u64(self.hash);
+        #[cfg(not(feature = "layout-cache"))]
+        unimplemented!()
+    }
+}
+
+impl Debug for PackedNode {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        self.node.fmt(f)
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 895430a25..b05a57b37 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -9,9 +9,9 @@
 //!   [module], consisting of a scope of values that were exported by the code
 //!   and a template with the contents of the module. This template can be
 //!   instantiated with a style to produce a layout tree, a high-level, fully
-//!   styled representation of the document. The nodes of this tree are
-//!   self-contained and order-independent and thus much better suited for
-//!   layouting than the raw markup.
+//!   styled representation, rooted in the [document node]. The nodes of this
+//!   tree are self-contained and order-independent and thus much better suited
+//!   for layouting than the raw markup.
 //! - **Layouting:** Next, the tree is [layouted] into a portable version of the
 //!   typeset document. The output of this is a collection of [`Frame`]s (one
 //!   per page), ready for exporting.
@@ -24,6 +24,7 @@
 //! [evaluate]: eval::eval
 //! [module]: eval::Module
 //! [layout tree]: layout::LayoutTree
+//! [document node]: library::DocumentNode
 //! [layouted]: layout::layout
 //! [PDF]: export::pdf
 
@@ -53,9 +54,9 @@ use crate::eval::{Module, Scope};
 use crate::font::FontStore;
 use crate::frame::Frame;
 use crate::image::ImageStore;
-use crate::layout::PageNode;
 #[cfg(feature = "layout-cache")]
 use crate::layout::{EvictionPolicy, LayoutCache};
+use crate::library::DocumentNode;
 use crate::loading::Loader;
 use crate::source::{SourceId, SourceStore};
 use crate::style::Style;
@@ -107,9 +108,9 @@ impl Context {
     }
 
     /// Execute a source file and produce the resulting page nodes.
-    pub fn execute(&mut self, id: SourceId) -> TypResult<Vec<PageNode>> {
+    pub fn execute(&mut self, id: SourceId) -> TypResult<DocumentNode> {
         let module = self.evaluate(id)?;
-        Ok(module.template.to_pages(&self.style))
+        Ok(module.template.to_document(&self.style))
     }
 
     /// Typeset a source file into a collection of layouted frames.
diff --git a/src/library/container.rs b/src/library/container.rs
index 4b52139fb..2bcbbd192 100644
--- a/src/library/container.rs
+++ b/src/library/container.rs
@@ -5,14 +5,13 @@ use super::{ShapeKind, ShapeNode};
 pub fn box_(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
     let width = args.named("width")?;
     let height = args.named("height")?;
-    let fill = args.named("fill")?;
     let body: Template = args.find().unwrap_or_default();
     Ok(Value::Template(Template::from_inline(move |style| {
         ShapeNode {
             shape: ShapeKind::Rect,
             width,
             height,
-            fill: fill.map(Paint::Color),
+            fill: None,
             child: Some(body.to_flow(style).pack()),
         }
     })))
diff --git a/src/library/document.rs b/src/library/document.rs
new file mode 100644
index 000000000..fe01d2df2
--- /dev/null
+++ b/src/library/document.rs
@@ -0,0 +1,16 @@
+use super::prelude::*;
+use super::PageNode;
+
+/// The root layout node, a document consisting of top-level page runs.
+#[derive(Debug, Hash)]
+pub struct DocumentNode {
+    /// The page runs.
+    pub pages: Vec<PageNode>,
+}
+
+impl DocumentNode {
+    /// Layout the document into a sequence of frames, one per page.
+    pub fn layout(&self, ctx: &mut LayoutContext) -> Vec<Rc<Frame>> {
+        self.pages.iter().flat_map(|node| node.layout(ctx)).collect()
+    }
+}
diff --git a/src/library/flow.rs b/src/library/flow.rs
index cc53d5207..c41fb62c6 100644
--- a/src/library/flow.rs
+++ b/src/library/flow.rs
@@ -48,7 +48,7 @@ pub struct FlowNode {
     pub children: Vec<FlowChild>,
 }
 
-impl BlockLevel for FlowNode {
+impl Layout for FlowNode {
     fn layout(
         &self,
         ctx: &mut LayoutContext,
@@ -63,8 +63,8 @@ impl BlockLevel for FlowNode {
 pub enum FlowChild {
     /// Vertical spacing between other children.
     Spacing(Spacing),
-    /// Any block node and how to align it in the flow.
-    Node(BlockNode, Align),
+    /// A node and how to align it in the flow.
+    Node(PackedNode, Align),
 }
 
 impl Debug for FlowChild {
@@ -157,8 +157,8 @@ impl<'a> FlowLayouter<'a> {
         self.items.push(FlowItem::Absolute(resolved));
     }
 
-    /// Layout a block node.
-    fn layout_node(&mut self, ctx: &mut LayoutContext, node: &BlockNode, align: Align) {
+    /// Layout a node.
+    fn layout_node(&mut self, ctx: &mut LayoutContext, node: &PackedNode, align: Align) {
         let frames = node.layout(ctx, &self.regions);
         let len = frames.len();
         for (i, frame) in frames.into_iter().enumerate() {
diff --git a/src/library/grid.rs b/src/library/grid.rs
index bafd639ca..692ed210f 100644
--- a/src/library/grid.rs
+++ b/src/library/grid.rs
@@ -58,7 +58,7 @@ pub struct GridNode {
     /// Defines sizing of gutter rows and columns between content.
     pub gutter: Spec<Vec<TrackSizing>>,
     /// The nodes to be arranged in a grid.
-    pub children: Vec<BlockNode>,
+    pub children: Vec<PackedNode>,
 }
 
 /// Defines how to size a grid cell along an axis.
@@ -72,7 +72,7 @@ pub enum TrackSizing {
     Fractional(Fractional),
 }
 
-impl BlockLevel for GridNode {
+impl Layout for GridNode {
     fn layout(
         &self,
         ctx: &mut LayoutContext,
@@ -92,7 +92,7 @@ impl BlockLevel for GridNode {
 /// Performs grid layout.
 struct GridLayouter<'a> {
     /// The children of the grid.
-    children: &'a [BlockNode],
+    children: &'a [PackedNode],
     /// Whether the grid should expand to fill the region.
     expand: Spec<bool>,
     /// The column tracks including gutter tracks.
@@ -591,7 +591,7 @@ impl<'a> GridLayouter<'a> {
     ///
     /// Returns `None` if it's a gutter cell.
     #[track_caller]
-    fn cell(&self, x: usize, y: usize) -> Option<&'a BlockNode> {
+    fn cell(&self, x: usize, y: usize) -> Option<&'a PackedNode> {
         assert!(x < self.cols.len());
         assert!(y < self.rows.len());
 
diff --git a/src/library/image.rs b/src/library/image.rs
index b51e4e70a..f93d4b548 100644
--- a/src/library/image.rs
+++ b/src/library/image.rs
@@ -36,23 +36,31 @@ pub struct ImageNode {
     pub height: Option<Linear>,
 }
 
-impl InlineLevel for ImageNode {
-    fn layout(&self, ctx: &mut LayoutContext, space: Length, base: Size) -> Frame {
+impl Layout for ImageNode {
+    fn layout(
+        &self,
+        ctx: &mut LayoutContext,
+        regions: &Regions,
+    ) -> Vec<Constrained<Rc<Frame>>> {
         let img = ctx.images.get(self.id);
         let pixel_size = Spec::new(img.width() as f64, img.height() as f64);
         let pixel_ratio = pixel_size.x / pixel_size.y;
 
-        let width = self.width.map(|w| w.resolve(base.w));
-        let height = self.height.map(|w| w.resolve(base.h));
+        let width = self.width.map(|w| w.resolve(regions.base.w));
+        let height = self.height.map(|w| w.resolve(regions.base.h));
+
+        let mut cts = Constraints::new(regions.expand);
+        cts.set_base_if_linear(regions.base, Spec::new(self.width, self.height));
 
         let size = match (width, height) {
             (Some(width), Some(height)) => Size::new(width, height),
             (Some(width), None) => Size::new(width, width / pixel_ratio),
             (None, Some(height)) => Size::new(height * pixel_ratio, height),
             (None, None) => {
-                if space.is_finite() {
+                cts.exact.x = Some(regions.current.w);
+                if regions.current.w.is_finite() {
                     // Fit to width.
-                    Size::new(space, space / pixel_ratio)
+                    Size::new(regions.current.w, regions.current.w / pixel_ratio)
                 } else {
                     // Unbounded width, we have to make up something,
                     // so it is 1pt per pixel.
@@ -63,6 +71,7 @@ impl InlineLevel for ImageNode {
 
         let mut frame = Frame::new(size, size.h);
         frame.push(Point::zero(), Element::Image(self.id, size));
-        frame
+
+        vec![frame.constrain(cts)]
     }
 }
diff --git a/src/library/mod.rs b/src/library/mod.rs
index 775fb51f3..f11e05f39 100644
--- a/src/library/mod.rs
+++ b/src/library/mod.rs
@@ -6,6 +6,7 @@
 mod align;
 mod container;
 mod deco;
+mod document;
 mod flow;
 mod grid;
 mod image;
@@ -36,6 +37,7 @@ pub use self::image::*;
 pub use align::*;
 pub use container::*;
 pub use deco::*;
+pub use document::*;
 pub use flow::*;
 pub use grid::*;
 pub use pad::*;
diff --git a/src/library/pad.rs b/src/library/pad.rs
index d17a4ca23..88f8c5622 100644
--- a/src/library/pad.rs
+++ b/src/library/pad.rs
@@ -16,7 +16,7 @@ pub fn pad(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
         bottom.or(all).unwrap_or_default(),
     );
 
-    Ok(Value::Template(Template::from_block(move |style| {
+    Ok(Value::Template(Template::from_inline(move |style| {
         PadNode {
             padding,
             child: body.to_flow(style).pack(),
@@ -30,10 +30,10 @@ pub struct PadNode {
     /// The amount of padding.
     pub padding: Sides<Linear>,
     /// The child node whose sides to pad.
-    pub child: BlockNode,
+    pub child: PackedNode,
 }
 
-impl BlockLevel for PadNode {
+impl Layout for PadNode {
     fn layout(
         &self,
         ctx: &mut LayoutContext,
diff --git a/src/library/page.rs b/src/library/page.rs
index 16e6283de..a5935002b 100644
--- a/src/library/page.rs
+++ b/src/library/page.rs
@@ -73,3 +73,23 @@ pub fn pagebreak(_: &mut EvalContext, _: &mut Args) -> TypResult<Value> {
     template.pagebreak(true);
     Ok(Value::Template(template))
 }
+
+/// Layouts its children onto one or multiple pages.
+#[derive(Debug, Hash)]
+pub struct PageNode {
+    /// The size of the page.
+    pub size: Size,
+    /// The node that produces the actual pages.
+    pub child: PackedNode,
+}
+
+impl PageNode {
+    /// Layout the page run into a sequence of frames, one per page.
+    pub fn layout(&self, ctx: &mut LayoutContext) -> Vec<Rc<Frame>> {
+        // When one of the lengths is infinite the page fits its content along
+        // that axis.
+        let expand = self.size.to_spec().map(Length::is_finite);
+        let regions = Regions::repeat(self.size, self.size, expand);
+        self.child.layout(ctx, &regions).into_iter().map(|c| c.item).collect()
+    }
+}
diff --git a/src/library/par.rs b/src/library/par.rs
index 216b7d410..c8befc2d0 100644
--- a/src/library/par.rs
+++ b/src/library/par.rs
@@ -8,7 +8,7 @@ use xi_unicode::LineBreakIterator;
 use super::prelude::*;
 use super::{shape, Decoration, ShapedText, Spacing};
 use crate::style::TextStyle;
-use crate::util::{EcoString, RangeExt, SliceExt};
+use crate::util::{EcoString, RangeExt, RcExt, SliceExt};
 
 /// `par`: Configure paragraphs.
 pub fn par(ctx: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
@@ -63,7 +63,7 @@ pub struct ParNode {
     pub children: Vec<ParChild>,
 }
 
-impl BlockLevel for ParNode {
+impl Layout for ParNode {
     fn layout(
         &self,
         ctx: &mut LayoutContext,
@@ -77,7 +77,7 @@ impl BlockLevel for ParNode {
 
         // Prepare paragraph layout by building a representation on which we can
         // do line breaking without layouting each and every line from scratch.
-        let layouter = ParLayouter::new(self, ctx, regions, bidi);
+        let layouter = ParLayouter::new(self, ctx, regions.clone(), bidi);
 
         // Find suitable linebreaks.
         layouter.layout(ctx, regions.clone())
@@ -126,7 +126,7 @@ pub enum ParChild {
     /// A run of text and how to align it in its line.
     Text(EcoString, Align, Rc<TextStyle>),
     /// Any child node and how to align it in its line.
-    Node(InlineNode, Align),
+    Node(PackedNode, Align),
     /// A decoration that applies until a matching `Undecorate`.
     Decorate(Decoration),
     /// The end of a decoration.
@@ -182,9 +182,12 @@ impl<'a> ParLayouter<'a> {
     fn new(
         par: &'a ParNode,
         ctx: &mut LayoutContext,
-        regions: &Regions,
+        mut regions: Regions,
         bidi: BidiInfo<'a>,
     ) -> Self {
+        // Disable expansion for children.
+        regions.expand = Spec::splat(false);
+
         let mut items = vec![];
         let mut ranges = vec![];
         let mut starts = vec![];
@@ -216,8 +219,8 @@ impl<'a> ParLayouter<'a> {
                     }
                 }
                 ParChild::Node(ref node, align) => {
-                    let frame = node.layout(ctx, regions.current.w, regions.base);
-                    items.push(ParItem::Frame(frame, align));
+                    let frame = node.layout(ctx, &regions).remove(0);
+                    items.push(ParItem::Frame(Rc::take(frame.item), align));
                     ranges.push(range);
                 }
                 ParChild::Decorate(ref deco) => {
diff --git a/src/library/shape.rs b/src/library/shape.rs
index 5be26aa49..c64dedb32 100644
--- a/src/library/shape.rs
+++ b/src/library/shape.rs
@@ -94,7 +94,7 @@ pub struct ShapeNode {
     /// How to fill the shape, if at all.
     pub fill: Option<Paint>,
     /// The child node to place into the shape, if any.
-    pub child: Option<BlockNode>,
+    pub child: Option<PackedNode>,
 }
 
 /// The type of a shape.
@@ -110,15 +110,36 @@ pub enum ShapeKind {
     Ellipse,
 }
 
-impl InlineLevel for ShapeNode {
-    fn layout(&self, ctx: &mut LayoutContext, space: Length, base: Size) -> Frame {
+impl Layout for ShapeNode {
+    fn layout(
+        &self,
+        ctx: &mut LayoutContext,
+        regions: &Regions,
+    ) -> Vec<Constrained<Rc<Frame>>> {
         // Resolve width and height relative to the region's base.
-        let width = self.width.map(|w| w.resolve(base.w));
-        let height = self.height.map(|h| h.resolve(base.h));
+        let width = self.width.map(|w| w.resolve(regions.base.w));
+        let height = self.height.map(|h| h.resolve(regions.base.h));
+
+        // Generate constraints.
+        let mut cts = Constraints::new(regions.expand);
+        cts.set_base_if_linear(regions.base, Spec::new(self.width, self.height));
+
+        // Set tight exact and base constraints if the child is
+        // automatically sized since we don't know what the child might do.
+        if self.width.is_none() {
+            cts.exact.x = Some(regions.current.w);
+            cts.base.x = Some(regions.base.w);
+        }
+
+        // Same here.
+        if self.height.is_none() {
+            cts.exact.y = Some(regions.current.h);
+            cts.base.y = Some(regions.base.h);
+        }
 
         // Layout.
         let mut frame = if let Some(child) = &self.child {
-            let mut node: &dyn BlockLevel = child;
+            let mut node: &dyn Layout = child;
 
             let padded;
             if matches!(self.shape, ShapeKind::Circle | ShapeKind::Ellipse) {
@@ -133,11 +154,14 @@ impl InlineLevel for ShapeNode {
 
             // The "pod" is the region into which the child will be layouted.
             let mut pod = {
-                let size = Size::new(width.unwrap_or(space), height.unwrap_or(base.h));
+                let size = Size::new(
+                    width.unwrap_or(regions.current.w),
+                    height.unwrap_or(regions.base.h),
+                );
 
                 let base = Size::new(
-                    if width.is_some() { size.w } else { base.w },
-                    if height.is_some() { size.h } else { base.h },
+                    if width.is_some() { size.w } else { regions.base.w },
+                    if height.is_some() { size.h } else { regions.base.h },
                 );
 
                 let expand = Spec::new(width.is_some(), height.is_some());
@@ -180,6 +204,6 @@ impl InlineLevel for ShapeNode {
             frame.prepend(pos, Element::Geometry(geometry, fill));
         }
 
-        frame
+        vec![frame.constrain(cts)]
     }
 }
diff --git a/src/library/stack.rs b/src/library/stack.rs
index fe1deda0f..46825939f 100644
--- a/src/library/stack.rs
+++ b/src/library/stack.rs
@@ -60,7 +60,7 @@ pub struct StackNode {
     pub children: Vec<StackChild>,
 }
 
-impl BlockLevel for StackNode {
+impl Layout for StackNode {
     fn layout(
         &self,
         ctx: &mut LayoutContext,
@@ -76,7 +76,7 @@ pub enum StackChild {
     /// Spacing between other nodes.
     Spacing(Spacing),
     /// Any block node and how to align it in the stack.
-    Node(BlockNode),
+    Node(PackedNode),
 }
 
 impl Debug for StackChild {
@@ -174,8 +174,8 @@ impl<'a> StackLayouter<'a> {
         self.items.push(StackItem::Absolute(resolved));
     }
 
-    /// Layout a block node.
-    fn layout_node(&mut self, ctx: &mut LayoutContext, node: &BlockNode) {
+    /// Layout a node.
+    fn layout_node(&mut self, ctx: &mut LayoutContext, node: &PackedNode) {
         let frames = node.layout(ctx, &self.regions);
         let len = frames.len();
         for (i, frame) in frames.into_iter().enumerate() {
diff --git a/src/library/transform.rs b/src/library/transform.rs
index b7e5e36c2..20d2bc1dc 100644
--- a/src/library/transform.rs
+++ b/src/library/transform.rs
@@ -1,5 +1,4 @@
 use super::prelude::*;
-use super::{ShapeKind, ShapeNode};
 
 /// `move`: Move content without affecting layout.
 pub fn move_(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
@@ -10,13 +9,7 @@ pub fn move_(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
     Ok(Value::Template(Template::from_inline(move |style| {
         MoveNode {
             offset: Spec::new(x, y),
-            child: ShapeNode {
-                shape: ShapeKind::Rect,
-                width: None,
-                height: None,
-                fill: None,
-                child: Some(body.to_flow(style).pack()),
-            },
+            child: body.to_flow(style).pack(),
         }
     })))
 }
@@ -24,21 +17,30 @@ pub fn move_(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
 #[derive(Debug, Hash)]
 struct MoveNode {
     offset: Spec<Option<Linear>>,
-    child: ShapeNode,
+    child: PackedNode,
 }
 
-impl InlineLevel for MoveNode {
-    fn layout(&self, ctx: &mut LayoutContext, space: Length, base: Size) -> Frame {
-        let offset = Point::new(
-            self.offset.x.map(|x| x.resolve(base.w)).unwrap_or_default(),
-            self.offset.y.map(|y| y.resolve(base.h)).unwrap_or_default(),
-        );
+impl Layout for MoveNode {
+    fn layout(
+        &self,
+        ctx: &mut LayoutContext,
+        regions: &Regions,
+    ) -> Vec<Constrained<Rc<Frame>>> {
+        let mut frames = self.child.layout(ctx, regions);
 
-        let mut frame = self.child.layout(ctx, space, base);
-        for (point, _) in &mut frame.children {
-            *point += offset;
+        for (Constrained { item: frame, .. }, (_, base)) in
+            frames.iter_mut().zip(regions.iter())
+        {
+            let offset = Point::new(
+                self.offset.x.map(|x| x.resolve(base.w)).unwrap_or_default(),
+                self.offset.y.map(|y| y.resolve(base.h)).unwrap_or_default(),
+            );
+
+            for (point, _) in &mut Rc::make_mut(frame).children {
+                *point += offset;
+            }
         }
 
-        frame
+        frames
     }
 }
diff --git a/src/main.rs b/src/main.rs
index b2ae1ea3a..fa8b61038 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -60,8 +60,8 @@ fn try_main() -> anyhow::Result<()> {
     // Typeset.
     match ctx.typeset(id) {
         // Export the PDF.
-        Ok(document) => {
-            let buffer = export::pdf(&ctx, &document);
+        Ok(frames) => {
+            let buffer = export::pdf(&ctx, &frames);
             fs::write(&args.output, buffer).context("failed to write PDF file")?;
         }
 
diff --git a/src/source.rs b/src/source.rs
index e692ac94d..74fa8d55b 100644
--- a/src/source.rs
+++ b/src/source.rs
@@ -1,4 +1,4 @@
-//! Source files.
+//! Source file management.
 
 use std::collections::HashMap;
 use std::io;
diff --git a/tests/ref/layout/pad.png b/tests/ref/layout/pad.png
index 4d381ce24..6ce4016a8 100644
Binary files a/tests/ref/layout/pad.png and b/tests/ref/layout/pad.png differ
diff --git a/tests/typ/layout/pad.typ b/tests/typ/layout/pad.typ
index 3729761a8..2a91d1ca7 100644
--- a/tests/typ/layout/pad.typ
+++ b/tests/typ/layout/pad.typ
@@ -11,19 +11,11 @@
   )
 )
 
-Hi #box(pad(left: 10pt)[]) there
+Hi #pad(left: 10pt)[A] there
 
 ---
-#let pad(body) = pad(left: 10pt, right: 10pt, body)
-
-// Pad inherits expansion behaviour from stack ....
-#pad[PL #align(right)[PR]]
-
-// ... block ...
-#block(pad[PL #align(right)[PR]])
-
-// ... and box.
-#box(pad[PL #align(right)[PR]])
+// Pad can grow.
+#pad(left: 10pt, right: 10pt)[PL #h(1fr) PR]
 
 ---
 // Test that the pad node doesn't consume the whole region.
diff --git a/tests/typ/layout/stack-2.typ b/tests/typ/layout/stack-2.typ
index afc9de394..2167f48f7 100644
--- a/tests/typ/layout/stack-2.typ
+++ b/tests/typ/layout/stack-2.typ
@@ -17,7 +17,7 @@ World! 🌍
 ---
 #page(height: 2cm)
 #font(white)
-#box(fill: forest)[
+#rect(fill: forest)[
           #v(1fr)
   #h(1fr) Hi you! #h(5pt)
           #v(5pt)
diff --git a/tests/typeset.rs b/tests/typeset.rs
index 68e56343c..aa4d250bb 100644
--- a/tests/typeset.rs
+++ b/tests/typeset.rs
@@ -19,7 +19,7 @@ use typst::geom::{
 use typst::image::Image;
 use typst::layout::layout;
 #[cfg(feature = "layout-cache")]
-use typst::layout::PageNode;
+use typst::library::DocumentNode;
 use typst::loading::FsLoader;
 use typst::parse::Scanner;
 use typst::source::SourceFile;
@@ -231,11 +231,11 @@ fn test_part(
 
     let mut ok = true;
     let (frames, mut errors) = match ctx.execute(id) {
-        Ok(tree) => {
-            let mut frames = layout(ctx, &tree);
+        Ok(document) => {
+            let mut frames = layout(ctx, &document);
 
             #[cfg(feature = "layout-cache")]
-            (ok &= test_incremental(ctx, i, &tree, &frames));
+            (ok &= test_incremental(ctx, i, &document, &frames));
 
             if !compare_ref {
                 frames.clear();
@@ -283,7 +283,7 @@ fn test_part(
 fn test_incremental(
     ctx: &mut Context,
     i: usize,
-    tree: &[PageNode],
+    document: &DocumentNode,
     frames: &[Rc<Frame>],
 ) -> bool {
     let mut ok = true;
@@ -298,7 +298,7 @@ fn test_incremental(
 
         ctx.layouts.turnaround();
 
-        let cached = layout(ctx, tree);
+        let cached = layout(ctx, document);
         let misses = ctx
             .layouts
             .entries()