Add delim-size parameter to mat, vec, and cases

Takes either a function or a relative length, just like with `lr`,
`stretch`, and `accent` which was changed in the previous two commits.
The default is now much clearer to the user: `x => x * 1.1 - 0.1em`.

crates/typst-cli/src/args.rs

@@ -491,7 +491,7 @@ pub enum PdfStandard {
     /// PDF/A-2u.
     #[value(name = "a-2u")]
     A_2u,
-    /// PDF/A-3u.
+    /// PDF/A-3b.
     #[value(name = "a-3b")]
     A_3b,
     /// PDF/A-3u.

crates/typst-kit/src/package.rs

@@ -199,7 +199,7 @@ impl PackageStorage {
         // The place at which the specific package version will live in the end.
         let package_dir = base_dir.join(format!("{}", spec.version));
 
-        // To prevent multiple Typst instances from interferring, we download
+        // To prevent multiple Typst instances from interfering, we download
         // into a temporary directory first and then move this directory to
         // its final destination.
         //

crates/typst-layout/src/inline/collect.rs

@@ -206,7 +206,7 @@ pub fn collect<'a>(
                     }
                     InlineItem::Frame(mut frame) => {
                         frame.modify(&FrameModifiers::get_in(styles));
-                        apply_baseline_shift(&mut frame, styles);
+                        apply_shift(&engine.world, &mut frame, styles);
                         collector.push_item(Item::Frame(frame));
                     }
                 }
@@ -221,7 +221,7 @@ pub fn collect<'a>(
                 let mut frame = layout_and_modify(styles, |styles| {
                     layout_box(elem, engine, loc, styles, region)
                 })?;
-                apply_baseline_shift(&mut frame, styles);
+                apply_shift(&engine.world, &mut frame, styles);
                 collector.push_item(Item::Frame(frame));
             }
         } else if let Some(elem) = child.to_packed::<TagElem>() {

crates/typst-layout/src/inline/line.rs

@@ -5,7 +5,7 @@ use typst_library::engine::Engine;
 use typst_library::introspection::{SplitLocator, Tag};
 use typst_library::layout::{Abs, Dir, Em, Fr, Frame, FrameItem, Point};
 use typst_library::model::ParLineMarker;
-use typst_library::text::{Lang, TextElem};
+use typst_library::text::{variant, Lang, TextElem};
 use typst_utils::Numeric;
 
 use super::*;
@@ -330,7 +330,7 @@ fn adjust_cj_at_line_start(p: &Preparation, items: &mut Items) {
         let glyph = shaped.glyphs.to_mut().first_mut().unwrap();
         let shrink = glyph.shrinkability().0;
         glyph.shrink_left(shrink);
-        shaped.width -= shrink.at(shaped.size);
+        shaped.width -= shrink.at(glyph.size);
     } else if p.config.cjk_latin_spacing
         && glyph.is_cj_script()
         && glyph.x_offset > Em::zero()
@@ -342,7 +342,7 @@ fn adjust_cj_at_line_start(p: &Preparation, items: &mut Items) {
         glyph.x_advance -= shrink;
         glyph.x_offset = Em::zero();
         glyph.adjustability.shrinkability.0 = Em::zero();
-        shaped.width -= shrink.at(shaped.size);
+        shaped.width -= shrink.at(glyph.size);
     }
 }
 
@@ -360,7 +360,7 @@ fn adjust_cj_at_line_end(p: &Preparation, items: &mut Items) {
         let shrink = glyph.shrinkability().1;
         let punct = shaped.glyphs.to_mut().last_mut().unwrap();
         punct.shrink_right(shrink);
-        shaped.width -= shrink.at(shaped.size);
+        shaped.width -= shrink.at(punct.size);
     } else if p.config.cjk_latin_spacing
         && glyph.is_cj_script()
         && (glyph.x_advance - glyph.x_offset) > Em::one()
@@ -371,7 +371,7 @@ fn adjust_cj_at_line_end(p: &Preparation, items: &mut Items) {
         let glyph = shaped.glyphs.to_mut().last_mut().unwrap();
         glyph.x_advance -= shrink;
         glyph.adjustability.shrinkability.1 = Em::zero();
-        shaped.width -= shrink.at(shaped.size);
+        shaped.width -= shrink.at(glyph.size);
     }
 }
 
@@ -412,9 +412,30 @@ fn should_repeat_hyphen(pred_line: &Line, text: &str) -> bool {
     }
 }
 
-/// Apply the current baseline shift to a frame.
-pub fn apply_baseline_shift(frame: &mut Frame, styles: StyleChain) {
-    frame.translate(Point::with_y(TextElem::baseline_in(styles)));
+/// Apply the current baseline shift and italic compensation to a frame.
+pub fn apply_shift<'a>(
+    world: &Tracked<'a, dyn World + 'a>,
+    frame: &mut Frame,
+    styles: StyleChain,
+) {
+    let mut baseline = TextElem::baseline_in(styles);
+    let mut compensation = Abs::zero();
+    if let Some(scripts) = TextElem::shift_settings_in(styles) {
+        let font_metrics = TextElem::font_in(styles)
+            .into_iter()
+            .find_map(|family| {
+                world
+                    .book()
+                    .select(family.as_str(), variant(styles))
+                    .and_then(|id| world.font(id))
+            })
+            .map_or(*scripts.kind.default_metrics(), |f| {
+                *scripts.kind.read_metrics(f.metrics())
+            });
+        baseline -= scripts.shift.unwrap_or(font_metrics.vertical_offset).resolve(styles);
+        compensation += font_metrics.horizontal_offset.resolve(styles);
+    }
+    frame.translate(Point::new(compensation, baseline));
 }
 
 /// Commit to a line and build its frame.
@@ -444,7 +465,7 @@ pub fn commit(
                 && TextElem::overhang_in(text.styles)
                 && (line.items.len() > 1 || text.glyphs.len() > 1)
             {
-                let amount = overhang(glyph.c) * glyph.x_advance.at(text.size);
+                let amount = overhang(glyph.c) * glyph.x_advance.at(glyph.size);
                 offset -= amount;
                 remaining += amount;
             }
@@ -458,7 +479,7 @@ pub fn commit(
                 && TextElem::overhang_in(text.styles)
                 && (line.items.len() > 1 || text.glyphs.len() > 1)
             {
-                let amount = overhang(glyph.c) * glyph.x_advance.at(text.size);
+                let amount = overhang(glyph.c) * glyph.x_advance.at(glyph.size);
                 remaining += amount;
             }
         }
@@ -519,7 +540,7 @@ pub fn commit(
                     let mut frame = layout_and_modify(*styles, |styles| {
                         layout_box(elem, engine, loc.relayout(), styles, region)
                     })?;
-                    apply_baseline_shift(&mut frame, *styles);
+                    apply_shift(&engine.world, &mut frame, *styles);
                     push(&mut offset, frame, idx);
                 } else {
                     offset += amount;

crates/typst-layout/src/inline/linebreak.rs

@@ -927,9 +927,9 @@ impl Estimates {
                     let byte_len = g.range.len();
                     let stretch = g.stretchability().0 + g.stretchability().1;
                     let shrink = g.shrinkability().0 + g.shrinkability().1;
-                    widths.push(byte_len, g.x_advance.at(shaped.size));
-                    stretchability.push(byte_len, stretch.at(shaped.size));
-                    shrinkability.push(byte_len, shrink.at(shaped.size));
+                    widths.push(byte_len, g.x_advance.at(g.size));
+                    stretchability.push(byte_len, stretch.at(g.size));
+                    shrinkability.push(byte_len, shrink.at(g.size));
                     justifiables.push(byte_len, g.is_justifiable() as usize);
                 }
             } else {

crates/typst-layout/src/inline/mod.rs

@@ -29,7 +29,7 @@ use typst_utils::{Numeric, SliceExt};
 use self::collect::{collect, Item, Segment, SpanMapper};
 use self::deco::decorate;
 use self::finalize::finalize;
-use self::line::{apply_baseline_shift, commit, line, Line};
+use self::line::{apply_shift, commit, line, Line};
 use self::linebreak::{linebreak, Breakpoint};
 use self::prepare::{prepare, Preparation};
 use self::shaping::{

crates/typst-layout/src/inline/prepare.rs

@@ -144,7 +144,7 @@ fn add_cjk_latin_spacing(items: &mut [(Range, Item)]) {
                 // The spacing is default to 1/4 em, and can be shrunk to 1/8 em.
                 glyph.x_advance += Em::new(0.25);
                 glyph.adjustability.shrinkability.1 += Em::new(0.125);
-                text.width += Em::new(0.25).at(text.size);
+                text.width += Em::new(0.25).at(glyph.size);
             }
 
             // Case 2: Latin followed by a CJ character
@@ -152,7 +152,7 @@ fn add_cjk_latin_spacing(items: &mut [(Range, Item)]) {
                 glyph.x_advance += Em::new(0.25);
                 glyph.x_offset += Em::new(0.25);
                 glyph.adjustability.shrinkability.0 += Em::new(0.125);
-                text.width += Em::new(0.25).at(text.size);
+                text.width += Em::new(0.25).at(glyph.size);
             }
 
             prev = Some(glyph);

crates/typst-layout/src/inline/shaping.rs

@@ -3,14 +3,15 @@ use std::fmt::{self, Debug, Formatter};
 use std::sync::Arc;
 
 use az::SaturatingAs;
-use rustybuzz::{BufferFlags, ShapePlan, UnicodeBuffer};
+use rustybuzz::{BufferFlags, Feature, ShapePlan, UnicodeBuffer};
+use ttf_parser::gsub::SubstitutionSubtable;
 use ttf_parser::Tag;
 use typst_library::engine::Engine;
 use typst_library::foundations::{Smart, StyleChain};
 use typst_library::layout::{Abs, Dir, Em, Frame, FrameItem, Point, Size};
 use typst_library::text::{
     families, features, is_default_ignorable, language, variant, Font, FontFamily,
-    FontVariant, Glyph, Lang, Region, TextEdgeBounds, TextElem, TextItem,
+    FontVariant, Glyph, Lang, Region, ShiftSettings, TextEdgeBounds, TextElem, TextItem,
 };
 use typst_library::World;
 use typst_utils::SliceExt;
@@ -41,8 +42,6 @@ pub struct ShapedText<'a> {
     pub styles: StyleChain<'a>,
     /// The font variant.
     pub variant: FontVariant,
-    /// The font size.
-    pub size: Abs,
     /// The width of the text's bounding box.
     pub width: Abs,
     /// The shaped glyphs.
@@ -62,6 +61,8 @@ pub struct ShapedGlyph {
     pub x_offset: Em,
     /// The vertical offset of the glyph.
     pub y_offset: Em,
+    /// The font size for the glyph.
+    pub size: Abs,
     /// The adjustability of the glyph.
     pub adjustability: Adjustability,
     /// The byte range of this glyph's cluster in the full inline layout. A
@@ -222,14 +223,17 @@ impl<'a> ShapedText<'a> {
         let mut frame = Frame::soft(size);
         frame.set_baseline(top);
 
+        let size = TextElem::size_in(self.styles);
         let shift = TextElem::baseline_in(self.styles);
         let decos = TextElem::deco_in(self.styles);
         let fill = TextElem::fill_in(self.styles);
         let stroke = TextElem::stroke_in(self.styles);
         let span_offset = TextElem::span_offset_in(self.styles);
 
-        for ((font, y_offset), group) in
-            self.glyphs.as_ref().group_by_key(|g| (g.font.clone(), g.y_offset))
+        for ((font, y_offset, glyph_size), group) in self
+            .glyphs
+            .as_ref()
+            .group_by_key(|g| (g.font.clone(), g.y_offset, g.size))
         {
             let mut range = group[0].range.clone();
             for glyph in group {
@@ -237,7 +241,7 @@ impl<'a> ShapedText<'a> {
                 range.end = range.end.max(glyph.range.end);
             }
 
-            let pos = Point::new(offset, top + shift - y_offset.at(self.size));
+            let pos = Point::new(offset, top + shift - y_offset.at(size));
             let glyphs: Vec<Glyph> = group
                 .iter()
                 .map(|shaped: &ShapedGlyph| {
@@ -257,11 +261,11 @@ impl<'a> ShapedText<'a> {
                         adjustability_right * justification_ratio;
                     if shaped.is_justifiable() {
                         justification_right +=
-                            Em::from_length(extra_justification, self.size)
+                            Em::from_abs(extra_justification, glyph_size)
                     }
 
-                    frame.size_mut().x += justification_left.at(self.size)
-                        + justification_right.at(self.size);
+                    frame.size_mut().x += justification_left.at(glyph_size)
+                        + justification_right.at(glyph_size);
 
                     // We may not be able to reach the offset completely if
                     // it exceeds u16, but better to have a roughly correct
@@ -304,7 +308,7 @@ impl<'a> ShapedText<'a> {
 
             let item = TextItem {
                 font,
-                size: self.size,
+                size: glyph_size,
                 lang: self.lang,
                 region: self.region,
                 fill: fill.clone(),
@@ -336,12 +340,13 @@ impl<'a> ShapedText<'a> {
         let mut top = Abs::zero();
         let mut bottom = Abs::zero();
 
+        let size = TextElem::size_in(self.styles);
         let top_edge = TextElem::top_edge_in(self.styles);
         let bottom_edge = TextElem::bottom_edge_in(self.styles);
 
         // Expand top and bottom by reading the font's vertical metrics.
         let mut expand = |font: &Font, bounds: TextEdgeBounds| {
-            let (t, b) = font.edges(top_edge, bottom_edge, self.size, bounds);
+            let (t, b) = font.edges(top_edge, bottom_edge, size, bounds);
             top.set_max(t);
             bottom.set_max(b);
         };
@@ -388,18 +393,16 @@ impl<'a> ShapedText<'a> {
     pub fn stretchability(&self) -> Abs {
         self.glyphs
             .iter()
-            .map(|g| g.stretchability().0 + g.stretchability().1)
-            .sum::<Em>()
-            .at(self.size)
+            .map(|g| (g.stretchability().0 + g.stretchability().1).at(g.size))
+            .sum()
     }
 
     /// The shrinkability of the text
     pub fn shrinkability(&self) -> Abs {
         self.glyphs
             .iter()
-            .map(|g| g.shrinkability().0 + g.shrinkability().1)
-            .sum::<Em>()
-            .at(self.size)
+            .map(|g| (g.shrinkability().0 + g.shrinkability().1).at(g.size))
+            .sum()
     }
 
     /// Reshape a range of the shaped text, reusing information from this
@@ -418,9 +421,8 @@ impl<'a> ShapedText<'a> {
                 lang: self.lang,
                 region: self.region,
                 styles: self.styles,
-                size: self.size,
                 variant: self.variant,
-                width: glyphs.iter().map(|g| g.x_advance).sum::<Em>().at(self.size),
+                width: glyphs_width(glyphs),
                 glyphs: Cow::Borrowed(glyphs),
             }
         } else {
@@ -484,13 +486,15 @@ impl<'a> ShapedText<'a> {
             // that subtracting either of the endpoints by self.base doesn't
             // underflow. See <https://github.com/typst/typst/issues/2283>.
             .unwrap_or_else(|| self.base..self.base);
-            self.width += x_advance.at(self.size);
+            let size = TextElem::size_in(self.styles);
+            self.width += x_advance.at(size);
             let glyph = ShapedGlyph {
                 font,
                 glyph_id: glyph_id.0,
                 x_advance,
                 x_offset: Em::zero(),
                 y_offset: Em::zero(),
+                size,
                 adjustability: Adjustability::default(),
                 range,
                 safe_to_break: true,
@@ -666,6 +670,7 @@ fn shape<'a>(
     region: Option<Region>,
 ) -> ShapedText<'a> {
     let size = TextElem::size_in(styles);
+    let shift_settings = TextElem::shift_settings_in(styles);
     let mut ctx = ShapingContext {
         engine,
         size,
@@ -676,6 +681,7 @@ fn shape<'a>(
         features: features(styles),
         fallback: TextElem::fallback_in(styles),
         dir,
+        shift_settings,
     };
 
     if !text.is_empty() {
@@ -698,12 +704,17 @@ fn shape<'a>(
         region,
         styles,
         variant: ctx.variant,
-        size,
-        width: ctx.glyphs.iter().map(|g| g.x_advance).sum::<Em>().at(size),
+        width: glyphs_width(&ctx.glyphs),
         glyphs: Cow::Owned(ctx.glyphs),
     }
 }
 
+/// Computes the width of a run of glyphs relative to the font size, accounting
+/// for their individual scaling factors and other font metrics.
+fn glyphs_width(glyphs: &[ShapedGlyph]) -> Abs {
+    glyphs.iter().map(|g| g.x_advance.at(g.size)).sum()
+}
+
 /// Holds shaping results and metadata common to all shaped segments.
 struct ShapingContext<'a, 'v> {
     engine: &'a Engine<'v>,
@@ -715,6 +726,7 @@ struct ShapingContext<'a, 'v> {
     features: Vec<rustybuzz::Feature>,
     fallback: bool,
     dir: Dir,
+    shift_settings: Option<ShiftSettings>,
 }
 
 /// Shape text with font fallback using the `families` iterator.
@@ -789,6 +801,18 @@ fn shape_segment<'a>(
     // text extraction.
     buffer.set_flags(BufferFlags::REMOVE_DEFAULT_IGNORABLES);
 
+    let (script_shift, script_compensation, scale, shift_feature) = ctx
+        .shift_settings
+        .map_or((Em::zero(), Em::zero(), Em::one(), None), |settings| {
+            determine_shift(text, &font, settings)
+        });
+
+    let has_shift_feature = shift_feature.is_some();
+    if let Some(feat) = shift_feature {
+        // Temporarily push the feature.
+        ctx.features.push(feat)
+    }
+
     // Prepare the shape plan. This plan depends on direction, script, language,
     // and features, but is independent from the text and can thus be memoized.
     let plan = create_shape_plan(
@@ -799,6 +823,10 @@ fn shape_segment<'a>(
         &ctx.features,
     );
 
+    if has_shift_feature {
+        ctx.features.pop();
+    }
+
     // Shape!
     let buffer = rustybuzz::shape_with_plan(font.rusty(), &plan, buffer);
     let infos = buffer.glyph_infos();
@@ -869,8 +897,9 @@ fn shape_segment<'a>(
                 glyph_id: info.glyph_id as u16,
                 // TODO: Don't ignore y_advance.
                 x_advance,
-                x_offset: font.to_em(pos[i].x_offset),
-                y_offset: font.to_em(pos[i].y_offset),
+                x_offset: font.to_em(pos[i].x_offset) + script_compensation,
+                y_offset: font.to_em(pos[i].y_offset) + script_shift,
+                size: scale.at(ctx.size),
                 adjustability: Adjustability::default(),
                 range: start..end,
                 safe_to_break: !info.unsafe_to_break(),
@@ -932,6 +961,64 @@ fn shape_segment<'a>(
     ctx.used.pop();
 }
 
+/// Returns a `(script_shift, script_compensation, scale, feature)` quadruplet
+/// describing how to produce scripts.
+///
+/// Those values determine how the rendered text should be transformed to
+/// display sub-/super-scripts. If the OpenType feature can be used, the
+/// rendered text should not be transformed in any way, and so those values are
+/// neutral (`(0, 0, 1, None)`). If scripts should be synthesized, those values
+/// determine how to transform the rendered text to display scripts as expected.
+fn determine_shift(
+    text: &str,
+    font: &Font,
+    settings: ShiftSettings,
+) -> (Em, Em, Em, Option<Feature>) {
+    settings
+        .typographic
+        .then(|| {
+            // If typographic scripts are enabled (i.e., we want to use the
+            // OpenType feature instead of synthesizing if possible), we add
+            // "subs"/"sups" to the feature list if supported by the font.
+            // In case of a problem, we just early exit
+            let gsub = font.rusty().tables().gsub?;
+            let subtable_index =
+                gsub.features.find(settings.kind.feature())?.lookup_indices.get(0)?;
+            let coverage = gsub
+                .lookups
+                .get(subtable_index)?
+                .subtables
+                .get::<SubstitutionSubtable>(0)?
+                .coverage();
+            text.chars()
+                .all(|c| {
+                    font.rusty().glyph_index(c).is_some_and(|i| coverage.contains(i))
+                })
+                .then(|| {
+                    // If we can use the OpenType feature, we can keep the text
+                    // as is.
+                    (
+                        Em::zero(),
+                        Em::zero(),
+                        Em::one(),
+                        Some(Feature::new(settings.kind.feature(), 1, ..)),
+                    )
+                })
+        })
+        // Reunite the cases where `typographic` is `false` or where using the
+        // OpenType feature would not work.
+        .flatten()
+        .unwrap_or_else(|| {
+            let script_metrics = settings.kind.read_metrics(font.metrics());
+            (
+                settings.shift.unwrap_or(script_metrics.vertical_offset),
+                script_metrics.horizontal_offset,
+                settings.size.unwrap_or(script_metrics.height),
+                None,
+            )
+        })
+}
+
 /// Create a shape plan.
 #[comemo::memoize]
 pub fn create_shape_plan(
@@ -963,6 +1050,7 @@ fn shape_tofus(ctx: &mut ShapingContext, base: usize, text: &str, font: Font) {
             x_advance,
             x_offset: Em::zero(),
             y_offset: Em::zero(),
+            size: ctx.size,
             adjustability: Adjustability::default(),
             range: start..end,
             safe_to_break: true,
@@ -985,9 +1073,8 @@ fn shape_tofus(ctx: &mut ShapingContext, base: usize, text: &str, font: Font) {
 
 /// Apply tracking and spacing to the shaped glyphs.
 fn track_and_space(ctx: &mut ShapingContext) {
-    let tracking = Em::from_length(TextElem::tracking_in(ctx.styles), ctx.size);
-    let spacing =
-        TextElem::spacing_in(ctx.styles).map(|abs| Em::from_length(abs, ctx.size));
+    let tracking = Em::from_abs(TextElem::tracking_in(ctx.styles), ctx.size);
+    let spacing = TextElem::spacing_in(ctx.styles).map(|abs| Em::from_abs(abs, ctx.size));
 
     let mut glyphs = ctx.glyphs.iter_mut().peekable();
     while let Some(glyph) = glyphs.next() {

crates/typst-layout/src/math/accent.rs

@@ -1,6 +1,6 @@
 use typst_library::diag::SourceResult;
 use typst_library::foundations::{Packed, StyleChain};
-use typst_library::layout::{Em, Frame, Point, Size};
+use typst_library::layout::{Frame, Point, Size};
 use typst_library::math::AccentElem;
 
 use super::{
@@ -8,9 +8,6 @@ use super::{
     MathFragment,
 };
 
-/// How much the accent can be shorter than the base.
-const ACCENT_SHORT_FALL: Em = Em::new(0.5);
-
 /// Lays out an [`AccentElem`].
 #[typst_macros::time(name = "math.accent", span = elem.span())]
 pub fn layout_accent(
@@ -45,11 +42,8 @@ pub fn layout_accent(
     let mut glyph =
         GlyphFragment::new_char(ctx.font, accent_styles, accent.0, elem.span())?;
 
-    // Forcing the accent to be at least as large as the base makes it too wide
-    // in many cases.
-    let width = elem.size(styles).relative_to(base.width());
-    let short_fall = ACCENT_SHORT_FALL.at(glyph.item.size);
-    glyph.stretch_horizontal(ctx, width - short_fall);
+    let width = elem.size(styles).resolve(ctx.engine, styles, base.width())?;
+    glyph.stretch_horizontal(ctx, width);
     let accent_attach = glyph.accent_attach.0;
     let accent = glyph.into_frame();
 

crates/typst-layout/src/math/attach.rs

@@ -1,8 +1,9 @@
 use typst_library::diag::SourceResult;
 use typst_library::foundations::{Packed, StyleChain, SymbolElem};
-use typst_library::layout::{Abs, Axis, Corner, Frame, Point, Rel, Size};
+use typst_library::layout::{Abs, Axis, Corner, Frame, Point, Size};
 use typst_library::math::{
     AttachElem, EquationElem, LimitsElem, PrimesElem, ScriptsElem, StretchElem,
+    StretchSize,
 };
 use typst_utils::OptionExt;
 
@@ -66,12 +67,12 @@ pub fn layout_attach(
         let relative_to_width = measure!(t, width).max(measure!(b, width));
         stretch_fragment(
             ctx,
+            styles,
             &mut base,
             Some(Axis::X),
             Some(relative_to_width),
-            stretch,
-            Abs::zero(),
-        );
+            &stretch,
+        )?;
     }
 
     let fragments = [
@@ -154,7 +155,7 @@ pub fn layout_limits(
 }
 
 /// Get the size to stretch the base to.
-fn stretch_size(styles: StyleChain, elem: &Packed<AttachElem>) -> Option<Rel<Abs>> {
+fn stretch_size(styles: StyleChain, elem: &Packed<AttachElem>) -> Option<StretchSize> {
     // Extract from an EquationElem.
     let mut base = &elem.base;
     while let Some(equation) = base.to_packed::<EquationElem>() {

crates/typst-layout/src/math/frac.rs

@@ -1,14 +1,13 @@
 use typst_library::diag::SourceResult;
 use typst_library::foundations::{Content, Packed, Resolve, StyleChain, SymbolElem};
 use typst_library::layout::{Em, Frame, FrameItem, Point, Size};
-use typst_library::math::{BinomElem, FracElem};
+use typst_library::math::{BinomElem, FracElem, DELIM_SHORT_FALL};
 use typst_library::text::TextElem;
 use typst_library::visualize::{FixedStroke, Geometry};
 use typst_syntax::Span;
 
 use super::{
-    style_for_denominator, style_for_numerator, FrameFragment, GlyphFragment,
-    MathContext, DELIM_SHORT_FALL,
+    style_for_denominator, style_for_numerator, FrameFragment, GlyphFragment, MathContext,
 };
 
 const FRAC_AROUND: Em = Em::new(0.1);
@@ -49,7 +48,7 @@ fn layout_frac_like(
     binom: bool,
     span: Span,
 ) -> SourceResult<()> {
-    let short_fall = DELIM_SHORT_FALL.resolve(styles);
+    let short_fall = DELIM_SHORT_FALL.abs().resolve(styles);
     let axis = scaled!(ctx, styles, axis_height);
     let thickness = scaled!(ctx, styles, fraction_rule_thickness);
     let shift_up = scaled!(

crates/typst-layout/src/math/fragment.rs

@@ -215,7 +215,7 @@ impl MathFragment {
                     &glyph.item.font,
                     GlyphId(glyph.item.glyphs[glyph_index].id),
                     corner,
-                    Em::from_length(height, glyph.item.size),
+                    Em::from_abs(height, glyph.item.size),
                 )
                 .unwrap_or_default()
                 .at(glyph.item.size)
@@ -767,8 +767,8 @@ fn assemble(
             advance += ratio * (max_overlap - min_overlap);
         }
         let (x, y) = match axis {
-            Axis::X => (Em::from_length(advance, base.item.size), Em::zero()),
-            Axis::Y => (Em::zero(), Em::from_length(advance, base.item.size)),
+            Axis::X => (Em::from_abs(advance, base.item.size), Em::zero()),
+            Axis::Y => (Em::zero(), Em::from_abs(advance, base.item.size)),
         };
         glyphs.push(Glyph {
             id: part.glyph_id.0,

crates/typst-layout/src/math/lr.rs

@@ -1,11 +1,11 @@
 use typst_library::diag::SourceResult;
 use typst_library::foundations::{Packed, StyleChain};
-use typst_library::layout::{Abs, Axis, Rel};
-use typst_library::math::{EquationElem, LrElem, MidElem};
+use typst_library::layout::{Abs, Axis};
+use typst_library::math::{EquationElem, LrElem, MidElem, StretchSize};
 use typst_utils::SliceExt;
 use unicode_math_class::MathClass;
 
-use super::{stretch_fragment, MathContext, MathFragment, DELIM_SHORT_FALL};
+use super::{stretch_fragment, MathContext, MathFragment};
 
 /// Lays out an [`LrElem`].
 #[typst_macros::time(name = "math.lr", span = elem.span())]
@@ -22,7 +22,7 @@ pub fn layout_lr(
 
     // Extract implicit LrElem.
     if let Some(lr) = body.to_packed::<LrElem>() {
-        if lr.size(styles).is_one() {
+        if lr.size(styles).is_lr_default() {
             body = &lr.body;
         }
     }
@@ -45,10 +45,24 @@ pub fn layout_lr(
 
     // Scale up fragments at both ends.
     match inner_fragments {
-        [one] => scale_if_delimiter(ctx, one, relative_to, height, None),
+        [one] => scale_if_delimiter(ctx, styles, one, relative_to, &height, None)?,
         [first, .., last] => {
-            scale_if_delimiter(ctx, first, relative_to, height, Some(MathClass::Opening));
-            scale_if_delimiter(ctx, last, relative_to, height, Some(MathClass::Closing));
+            scale_if_delimiter(
+                ctx,
+                styles,
+                first,
+                relative_to,
+                &height,
+                Some(MathClass::Opening),
+            )?;
+            scale_if_delimiter(
+                ctx,
+                styles,
+                last,
+                relative_to,
+                &height,
+                Some(MathClass::Closing),
+            )?;
         }
         [] => {}
     }
@@ -58,7 +72,7 @@ pub fn layout_lr(
         if let MathFragment::Glyph(ref mut glyph) = fragment {
             if glyph.mid_stretched == Some(false) {
                 glyph.mid_stretched = Some(true);
-                scale(ctx, fragment, relative_to, height);
+                scale(ctx, styles, fragment, relative_to, &height)?;
             }
         }
     }
@@ -112,32 +126,32 @@ pub fn layout_mid(
 /// it is a delimiter, in a way that cannot be overridden by the user.
 fn scale_if_delimiter(
     ctx: &mut MathContext,
+    styles: StyleChain,
     fragment: &mut MathFragment,
     relative_to: Abs,
-    height: Rel<Abs>,
+    height: &StretchSize,
     apply: Option<MathClass>,
-) {
+) -> SourceResult<()> {
     if matches!(
         fragment.class(),
         MathClass::Opening | MathClass::Closing | MathClass::Fence
     ) {
-        scale(ctx, fragment, relative_to, height);
+        scale(ctx, styles, fragment, relative_to, height)?;
 
         if let Some(class) = apply {
             fragment.set_class(class);
         }
     }
+    Ok(())
 }
 
 /// Scales a math fragment to a height.
 fn scale(
     ctx: &mut MathContext,
+    styles: StyleChain,
     fragment: &mut MathFragment,
     relative_to: Abs,
-    height: Rel<Abs>,
-) {
-    // This unwrap doesn't really matter. If it is None, then the fragment
-    // won't be stretchable anyways.
-    let short_fall = DELIM_SHORT_FALL.at(fragment.font_size().unwrap_or_default());
-    stretch_fragment(ctx, fragment, Some(Axis::Y), Some(relative_to), height, short_fall);
+    height: &StretchSize,
+) -> SourceResult<()> {
+    stretch_fragment(ctx, styles, fragment, Some(Axis::Y), Some(relative_to), height)
 }

crates/typst-layout/src/math/mat.rs

@@ -1,19 +1,20 @@
 use typst_library::diag::{bail, warning, SourceResult};
 use typst_library::foundations::{Content, Packed, Resolve, StyleChain};
 use typst_library::layout::{
-    Abs, Axes, Em, FixedAlignment, Frame, FrameItem, Point, Ratio, Rel, Size,
+    Abs, Axes, Em, FixedAlignment, Frame, FrameItem, Point, Rel, Size,
+};
+use typst_library::math::{
+    Augment, AugmentOffsets, CasesElem, MatElem, StretchSize, VecElem,
 };
-use typst_library::math::{Augment, AugmentOffsets, CasesElem, MatElem, VecElem};
 use typst_library::text::TextElem;
 use typst_library::visualize::{FillRule, FixedStroke, Geometry, LineCap, Shape};
 use typst_syntax::Span;
 
 use super::{
     alignments, style_for_denominator, AlignmentResult, FrameFragment, GlyphFragment,
-    LeftRightAlternator, MathContext, DELIM_SHORT_FALL,
+    LeftRightAlternator, MathContext,
 };
 
-const VERTICAL_PADDING: Ratio = Ratio::new(0.1);
 const DEFAULT_STROKE_THICKNESS: Em = Em::new(0.05);
 
 /// Lays out a [`VecElem`].
@@ -39,7 +40,15 @@ pub fn layout_vec(
     )?;
 
     let delim = elem.delim(styles);
-    layout_delimiters(ctx, styles, frame, delim.open(), delim.close(), span)
+    layout_delimiters(
+        ctx,
+        styles,
+        frame,
+        &elem.delim_size(styles),
+        delim.open(),
+        delim.close(),
+        span,
+    )
 }
 
 /// Lays out a [`CasesElem`].
@@ -67,7 +76,7 @@ pub fn layout_cases(
     let delim = elem.delim(styles);
     let (open, close) =
         if elem.reverse(styles) { (None, delim.close()) } else { (delim.open(), None) };
-    layout_delimiters(ctx, styles, frame, open, close, span)
+    layout_delimiters(ctx, styles, frame, &elem.delim_size(styles), open, close, span)
 }
 
 /// Lays out a [`MatElem`].
@@ -125,7 +134,15 @@ pub fn layout_mat(
     )?;
 
     let delim = elem.delim(styles);
-    layout_delimiters(ctx, styles, frame, delim.open(), delim.close(), span)
+    layout_delimiters(
+        ctx,
+        styles,
+        frame,
+        &elem.delim_size(styles),
+        delim.open(),
+        delim.close(),
+        span,
+    )
 }
 
 /// Layout the inner contents of a matrix, vector, or cases.
@@ -306,19 +323,20 @@ fn layout_delimiters(
     ctx: &mut MathContext,
     styles: StyleChain,
     mut frame: Frame,
+    size: &StretchSize,
     left: Option<char>,
     right: Option<char>,
     span: Span,
 ) -> SourceResult<()> {
-    let short_fall = DELIM_SHORT_FALL.resolve(styles);
     let axis = scaled!(ctx, styles, axis_height);
     let height = frame.height();
-    let target = height + VERTICAL_PADDING.of(height);
     frame.set_baseline(height / 2.0 + axis);
 
+    let target = size.resolve(ctx.engine, styles, height)?;
+
     if let Some(left_c) = left {
         let mut left = GlyphFragment::new_char(ctx.font, styles, left_c, span)?;
-        left.stretch_vertical(ctx, target - short_fall);
+        left.stretch_vertical(ctx, target);
         left.center_on_axis();
         ctx.push(left);
     }
@@ -327,7 +345,7 @@ fn layout_delimiters(
 
     if let Some(right_c) = right {
         let mut right = GlyphFragment::new_char(ctx.font, styles, right_c, span)?;
-        right.stretch_vertical(ctx, target - short_fall);
+        right.stretch_vertical(ctx, target);
         right.center_on_axis();
         ctx.push(right);
     }

crates/typst-layout/src/math/shared.rs

@@ -1,7 +1,7 @@
 use ttf_parser::math::MathValue;
 use ttf_parser::Tag;
 use typst_library::foundations::{Style, StyleChain};
-use typst_library::layout::{Abs, Em, FixedAlignment, Frame, Point, Size};
+use typst_library::layout::{Abs, FixedAlignment, Frame, Point, Size};
 use typst_library::math::{EquationElem, MathSize};
 use typst_library::text::{FontFeatures, TextElem};
 use typst_utils::LazyHash;
@@ -30,9 +30,6 @@ macro_rules! percent {
     };
 }
 
-/// How much less high scaled delimiters can be than what they wrap.
-pub const DELIM_SHORT_FALL: Em = Em::new(0.1);
-
 /// Converts some unit to an absolute length with the current font & font size.
 pub trait Scaled {
     fn scaled(self, ctx: &MathContext, font_size: Abs) -> Abs;

crates/typst-layout/src/math/stretch.rs

@@ -1,7 +1,7 @@
 use typst_library::diag::{warning, SourceResult};
 use typst_library::foundations::{Packed, StyleChain};
-use typst_library::layout::{Abs, Axis, Rel};
-use typst_library::math::StretchElem;
+use typst_library::layout::{Abs, Axis};
+use typst_library::math::{StretchElem, StretchSize};
 use typst_utils::Get;
 
 use super::{stretch_axes, MathContext, MathFragment};
@@ -14,7 +14,7 @@ pub fn layout_stretch(
     styles: StyleChain,
 ) -> SourceResult<()> {
     let mut fragment = ctx.layout_into_fragment(&elem.body, styles)?;
-    stretch_fragment(ctx, &mut fragment, None, None, elem.size(styles), Abs::zero());
+    stretch_fragment(ctx, styles, &mut fragment, None, None, &elem.size(styles))?;
     ctx.push(fragment);
     Ok(())
 }
@@ -22,29 +22,29 @@ pub fn layout_stretch(
 /// Attempts to stretch the given fragment by/to the amount given in stretch.
 pub fn stretch_fragment(
     ctx: &mut MathContext,
+    styles: StyleChain,
     fragment: &mut MathFragment,
     axis: Option<Axis>,
     relative_to: Option<Abs>,
-    stretch: Rel<Abs>,
-    short_fall: Abs,
-) {
+    stretch: &StretchSize,
+) -> SourceResult<()> {
     let size = fragment.size();
 
-    let MathFragment::Glyph(ref mut glyph) = fragment else { return };
+    let MathFragment::Glyph(ref mut glyph) = fragment else { return Ok(()) };
 
     // Return if we attempt to stretch along an axis which isn't stretchable,
     // so that the original fragment isn't modified.
     let axes = stretch_axes(&glyph.item.font, glyph.base_glyph.id);
     let stretch_axis = if let Some(axis) = axis {
         if !axes.get(axis) {
-            return;
+            return Ok(());
         }
         axis
     } else {
         match (axes.x, axes.y) {
             (true, false) => Axis::X,
             (false, true) => Axis::Y,
-            (false, false) => return,
+            (false, false) => return Ok(()),
             (true, true) => {
                 // As far as we know, there aren't any glyphs that have both
                 // vertical and horizontal constructions. So for the time being, we
@@ -55,16 +55,19 @@ pub fn stretch_fragment(
                    hint: "this is probably a font bug";
                    hint: "please file an issue at https://github.com/typst/typst/issues"
                 ));
-                return;
+                return Ok(());
             }
         }
     };
 
     let relative_to_size = relative_to.unwrap_or_else(|| size.get(stretch_axis));
+    let target = stretch.resolve(ctx.engine, styles, relative_to_size)?;
 
-    glyph.stretch(ctx, stretch.relative_to(relative_to_size) - short_fall, stretch_axis);
+    glyph.stretch(ctx, target, stretch_axis);
 
     if stretch_axis == Axis::Y {
         glyph.center_on_axis();
     }
+
+    Ok(())
 }

crates/typst-library/src/foundations/array.rs

@@ -94,7 +94,7 @@ impl Array {
     }
 
     /// Iterate over references to the contained values.
-    pub fn iter(&self) -> std::slice::Iter<Value> {
+    pub fn iter(&self) -> std::slice::Iter<'_, Value> {
         self.0.iter()
     }
 
@@ -604,7 +604,7 @@ impl Array {
         Ok(acc)
     }
 
-    /// Calculates the product all items (works for all types that can be
+    /// Calculates the product of all items (works for all types that can be
     /// multiplied).
     #[func]
     pub fn product(

crates/typst-library/src/foundations/calc.rs

@@ -207,9 +207,9 @@ pub fn sqrt(
 /// ```
 #[func]
 pub fn root(
-    /// The expression to take the root of
+    /// The expression to take the root of.
     radicand: f64,
-    /// Which root of the radicand to take
+    /// Which root of the radicand to take.
     index: Spanned<i64>,
 ) -> SourceResult<f64> {
     if index.v == 0 {
@@ -317,7 +317,7 @@ pub fn asin(
 /// ```
 #[func(title = "Arccosine")]
 pub fn acos(
-    /// The number whose arcsine to calculate. Must be between -1 and 1.
+    /// The number whose arccosine to calculate. Must be between -1 and 1.
     value: Spanned<Num>,
 ) -> SourceResult<Angle> {
     let val = value.v.float();
@@ -387,7 +387,7 @@ pub fn cosh(
     value.cosh()
 }
 
-/// Calculates the hyperbolic tangent of an hyperbolic angle.
+/// Calculates the hyperbolic tangent of a hyperbolic angle.
 ///
 /// ```example
 /// #calc.tanh(0) \

crates/typst-library/src/foundations/dict.rs

@@ -114,7 +114,7 @@ impl Dict {
     }
 
     /// Iterate over pairs of references to the contained keys and values.
-    pub fn iter(&self) -> indexmap::map::Iter<Str, Value> {
+    pub fn iter(&self) -> indexmap::map::Iter<'_, Str, Value> {
         self.0.iter()
     }
 

crates/typst-library/src/layout/container.rs

@@ -497,7 +497,8 @@ mod callbacks {
 
     macro_rules! callback {
         ($name:ident = ($($param:ident: $param_ty:ty),* $(,)?) -> $ret:ty) => {
-            #[derive(Debug, Clone, PartialEq, Hash)]
+            #[derive(Debug, Clone, Hash)]
+            #[allow(clippy::derived_hash_with_manual_eq)]
             pub struct $name {
                 captured: Content,
                 f: fn(&Content, $($param_ty),*) -> $ret,
@@ -535,6 +536,19 @@ mod callbacks {
                     (self.f)(&self.captured, $($param),*)
                 }
             }
+
+            impl PartialEq for $name {
+                fn eq(&self, other: &Self) -> bool {
+                    // Comparing function pointers is problematic. Since for
+                    // each type of content, there is typically just one
+                    // callback, we skip it. It barely matters anyway since
+                    // getting into a comparison codepath for inline & block
+                    // elements containing callback bodies is close to
+                    // impossible (as these are generally generated in show
+                    // rules).
+                    self.captured.eq(&other.captured)
+                }
+            }
         };
     }
 

crates/typst-library/src/layout/em.rs

@@ -6,7 +6,7 @@ use ecow::EcoString;
 use typst_utils::{Numeric, Scalar};
 
 use crate::foundations::{cast, repr, Repr, Resolve, StyleChain, Value};
-use crate::layout::Abs;
+use crate::layout::{Abs, Length};
 use crate::text::TextElem;
 
 /// A length that is relative to the font size.
@@ -26,18 +26,18 @@ impl Em {
         Self(Scalar::ONE)
     }
 
-    /// Create a font-relative length.
+    /// Creates a font-relative length.
     pub const fn new(em: f64) -> Self {
         Self(Scalar::new(em))
     }
 
-    /// Create an em length from font units at the given units per em.
+    /// Creates an em length from font units at the given units per em.
     pub fn from_units(units: impl Into<f64>, units_per_em: f64) -> Self {
         Self(Scalar::new(units.into() / units_per_em))
     }
 
-    /// Create an em length from a length at the given font size.
-    pub fn from_length(length: Abs, font_size: Abs) -> Self {
+    /// Creates an em length from an absolute length at the given font size.
+    pub fn from_abs(length: Abs, font_size: Abs) -> Self {
         let result = length / font_size;
         if result.is_finite() {
             Self(Scalar::new(result))
@@ -46,6 +46,11 @@ impl Em {
         }
     }
 
+    /// Creates an em length from a length at the given font size.
+    pub fn from_length(length: Length, font_size: Abs) -> Em {
+        length.em + Self::from_abs(length.abs, font_size)
+    }
+
     /// The number of em units.
     pub const fn get(self) -> f64 {
         (self.0).get()
@@ -56,7 +61,7 @@ impl Em {
         Self::new(self.get().abs())
     }
 
-    /// Convert to an absolute length at the given font size.
+    /// Converts to an absolute length at the given font size.
     pub fn at(self, font_size: Abs) -> Abs {
         let resolved = font_size * self.get();
         if resolved.is_finite() {

crates/typst-library/src/layout/fragment.rs

@@ -47,12 +47,12 @@ impl Fragment {
     }
 
     /// Iterate over the contained frames.
-    pub fn iter(&self) -> std::slice::Iter<Frame> {
+    pub fn iter(&self) -> std::slice::Iter<'_, Frame> {
         self.0.iter()
     }
 
     /// Iterate over the contained frames.
-    pub fn iter_mut(&mut self) -> std::slice::IterMut<Frame> {
+    pub fn iter_mut(&mut self) -> std::slice::IterMut<'_, Frame> {
         self.0.iter_mut()
     }
 }

crates/typst-library/src/math/accent.rs

@@ -6,9 +6,21 @@ use icu_provider::AsDeserializingBufferProvider;
 use icu_provider_blob::BlobDataProvider;
 
 use crate::diag::bail;
-use crate::foundations::{cast, elem, func, Content, NativeElement, SymbolElem};
-use crate::layout::{Length, Rel};
-use crate::math::Mathy;
+use crate::foundations::{
+    cast, elem, func, Content, NativeElement, NativeFunc, SymbolElem,
+};
+use crate::layout::{Em, Length, Ratio, Rel};
+use crate::math::{Mathy, StretchSize};
+
+const ACCENT_SHORT_FALL: Em = Em::new(-0.5);
+
+#[func(name = "x => x - 0.5em")]
+const fn default_accent_size(base: Length) -> Rel {
+    Rel {
+        rel: Ratio::zero(),
+        abs: Length { abs: base.abs, em: ACCENT_SHORT_FALL },
+    }
+}
 
 /// Attaches an accent to a base.
 ///
@@ -59,12 +71,14 @@ pub struct AccentElem {
 
     /// The size of the accent, relative to the width of the base.
     ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
+    ///
     /// ```example
     /// $dash(A, size: #150%)$
     /// ```
-    #[resolve]
-    #[default(Rel::one())]
-    pub size: Rel<Length>,
+    #[default(<default_accent_size>::data().into())]
+    pub size: StretchSize,
 
     /// Whether to remove the dot on top of lowercase i and j when adding a top
     /// accent.
@@ -141,8 +155,11 @@ macro_rules! accents {
                 /// The base to which the accent is applied.
                 base: Content,
                 /// The size of the accent, relative to the width of the base.
+                ///
+                /// See the [stretch documentation]($math.stretch.size) for
+                /// more information on sizes.
                 #[named]
-                size: Option<Rel<Length>>,
+                size: Option<StretchSize>,
                 /// Whether to remove the dot on top of lowercase i and j when
                 /// adding a top accent.
                 #[named]

crates/typst-library/src/math/attach.rs

@@ -1,5 +1,4 @@
 use crate::foundations::{elem, Content, Packed};
-use crate::layout::{Length, Rel};
 use crate::math::{EquationElem, Mathy};
 
 /// A base with optional attachments.
@@ -128,31 +127,3 @@ pub struct LimitsElem {
     #[default(true)]
     pub inline: bool,
 }
-
-/// Stretches a glyph.
-///
-/// This function can also be used to automatically stretch the base of an
-/// attachment, so that it fits the top and bottom attachments.
-///
-/// Note that only some glyphs can be stretched, and which ones can depend on
-/// the math font being used. However, most math fonts are the same in this
-/// regard.
-///
-/// ```example
-/// $ H stretch(=)^"define" U + p V $
-/// $ f : X stretch(->>, size: #150%)_"surjective" Y $
-/// $ x stretch(harpoons.ltrb, size: #3em) y
-///     stretch(\[, size: #150%) z $
-/// ```
-#[elem(Mathy)]
-pub struct StretchElem {
-    /// The glyph to stretch.
-    #[required]
-    pub body: Content,
-
-    /// The size to stretch to, relative to the maximum size of the glyph and
-    /// its attachments.
-    #[resolve]
-    #[default(Rel::one())]
-    pub size: Rel<Length>,
-}

crates/typst-library/src/math/lr.rs

@@ -1,6 +1,16 @@
-use crate::foundations::{elem, func, Content, NativeElement, SymbolElem};
-use crate::layout::{Length, Rel};
-use crate::math::Mathy;
+use crate::foundations::{elem, func, Content, NativeElement, NativeFunc, SymbolElem};
+use crate::layout::{Em, Length, Ratio, Rel};
+use crate::math::{Mathy, StretchSize};
+
+pub const DELIM_SHORT_FALL: Em = Em::new(-0.1);
+
+#[func(name = "x => x - 0.1em")]
+pub const fn default_lr_size(base: Length) -> Rel {
+    Rel {
+        rel: Ratio::zero(),
+        abs: Length { abs: base.abs, em: DELIM_SHORT_FALL },
+    }
+}
 
 /// Scales delimiters.
 ///
@@ -8,10 +18,13 @@ use crate::math::Mathy;
 /// unmatched delimiters and to control the delimiter scaling more precisely.
 #[elem(title = "Left/Right", Mathy)]
 pub struct LrElem {
-    /// The size of the brackets, relative to the height of the wrapped content.
-    #[resolve]
-    #[default(Rel::one())]
-    pub size: Rel<Length>,
+    /// The size of the delimiters, relative to the height of the wrapped
+    /// content.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
+    #[default(<default_lr_size>::data().into())]
+    pub size: StretchSize,
 
     /// The delimited content, including the delimiters.
     #[required]
@@ -43,9 +56,13 @@ pub struct MidElem {
 /// ```
 #[func]
 pub fn floor(
-    /// The size of the brackets, relative to the height of the wrapped content.
+    /// The size of the delimiters, relative to the height of the wrapped
+    /// content.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
     #[named]
-    size: Option<Rel<Length>>,
+    size: Option<StretchSize>,
     /// The expression to floor.
     body: Content,
 ) -> Content {
@@ -59,9 +76,13 @@ pub fn floor(
 /// ```
 #[func]
 pub fn ceil(
-    /// The size of the brackets, relative to the height of the wrapped content.
+    /// The size of the delimiters, relative to the height of the wrapped
+    /// content.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
     #[named]
-    size: Option<Rel<Length>>,
+    size: Option<StretchSize>,
     /// The expression to ceil.
     body: Content,
 ) -> Content {
@@ -75,9 +96,13 @@ pub fn ceil(
 /// ```
 #[func]
 pub fn round(
-    /// The size of the brackets, relative to the height of the wrapped content.
+    /// The size of the delimiters, relative to the height of the wrapped
+    /// content.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
     #[named]
-    size: Option<Rel<Length>>,
+    size: Option<StretchSize>,
     /// The expression to round.
     body: Content,
 ) -> Content {
@@ -91,9 +116,13 @@ pub fn round(
 /// ```
 #[func]
 pub fn abs(
-    /// The size of the brackets, relative to the height of the wrapped content.
+    /// The size of the delimiters, relative to the height of the wrapped
+    /// content.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
     #[named]
-    size: Option<Rel<Length>>,
+    size: Option<StretchSize>,
     /// The expression to take the absolute value of.
     body: Content,
 ) -> Content {
@@ -107,9 +136,13 @@ pub fn abs(
 /// ```
 #[func]
 pub fn norm(
-    /// The size of the brackets, relative to the height of the wrapped content.
+    /// The size of the delimiters, relative to the height of the wrapped
+    /// content.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
     #[named]
-    size: Option<Rel<Length>>,
+    size: Option<StretchSize>,
     /// The expression to take the norm of.
     body: Content,
 ) -> Content {
@@ -120,7 +153,7 @@ fn delimited(
     body: Content,
     left: char,
     right: char,
-    size: Option<Rel<Length>>,
+    size: Option<StretchSize>,
 ) -> Content {
     let span = body.span();
     let mut elem = LrElem::new(Content::sequence([

crates/typst-library/src/math/matrix.rs

@@ -5,15 +5,27 @@ use unicode_math_class::MathClass;
 
 use crate::diag::{bail, At, HintedStrResult, StrResult};
 use crate::foundations::{
-    array, cast, dict, elem, Array, Content, Dict, Fold, NoneValue, Resolve, Smart,
-    StyleChain, Symbol, Value,
+    array, cast, dict, elem, func, Array, Content, Dict, Fold, NativeFunc, NoneValue,
+    Resolve, Smart, StyleChain, Symbol, Value,
 };
-use crate::layout::{Abs, Em, HAlignment, Length, Rel};
-use crate::math::Mathy;
+use crate::layout::{Abs, Em, HAlignment, Length, Ratio, Rel};
+use crate::math::{Mathy, StretchSize, DELIM_SHORT_FALL};
 use crate::visualize::Stroke;
 
 const DEFAULT_ROW_GAP: Em = Em::new(0.2);
 const DEFAULT_COL_GAP: Em = Em::new(0.5);
+const VERTICAL_PADDING: Ratio = Ratio::new(1.1);
+
+#[func(name = "x => x * 1.1 - 0.1em")]
+const fn default_mat_size(base: Length) -> Rel {
+    Rel {
+        rel: Ratio::zero(),
+        abs: Length {
+            abs: Abs::raw(base.abs.to_raw() * VERTICAL_PADDING.get()),
+            em: DELIM_SHORT_FALL,
+        },
+    }
+}
 
 /// A column vector.
 ///
@@ -40,6 +52,13 @@ pub struct VecElem {
     #[default(DelimiterPair::PAREN)]
     pub delim: DelimiterPair,
 
+    /// The size of the delimiters, relative to the elements' total height.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
+    #[default(<default_mat_size>::data().into())]
+    pub delim_size: StretchSize,
+
     /// The horizontal alignment that each element should have.
     ///
     /// ```example
@@ -101,6 +120,13 @@ pub struct MatElem {
     #[default(DelimiterPair::PAREN)]
     pub delim: DelimiterPair,
 
+    /// The size of the delimiters, relative to the cells' total height.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
+    #[default(<default_mat_size>::data().into())]
+    pub delim_size: StretchSize,
+
     /// The horizontal alignment that each cell should have.
     ///
     /// ```example
@@ -244,6 +270,13 @@ pub struct CasesElem {
     #[default(DelimiterPair::BRACE)]
     pub delim: DelimiterPair,
 
+    /// The size of the delimiters, relative to the branches' total height.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
+    #[default(<default_mat_size>::data().into())]
+    pub delim_size: StretchSize,
+
     /// Whether the direction of cases should be reversed.
     ///
     /// ```example

crates/typst-library/src/math/mod.rs

@@ -9,6 +9,7 @@ mod lr;
 mod matrix;
 mod op;
 mod root;
+mod stretch;
 mod style;
 mod underover;
 
@@ -21,6 +22,7 @@ pub use self::lr::*;
 pub use self::matrix::*;
 pub use self::op::*;
 pub use self::root::*;
+pub use self::stretch::*;
 pub use self::style::*;
 pub use self::underover::*;
 

crates/typst-library/src/math/stretch.rs

@@ -0,0 +1,125 @@
+use comemo::Track;
+
+use crate::diag::{At, SourceResult};
+use crate::engine::Engine;
+use crate::foundations::{
+    cast, elem, Content, Context, Func, NativeFunc, NativeFuncData, Resolve, StyleChain,
+};
+use crate::layout::{Abs, Rel};
+use crate::math::{default_lr_size, Mathy};
+
+/// Stretches a glyph.
+///
+/// This function can also be used to automatically stretch the base of an
+/// attachment, so that it fits the top and bottom attachments.
+///
+/// Note that only some glyphs can be stretched, and which ones can depend on
+/// the math font being used. However, most math fonts are the same in this
+/// regard.
+///
+/// ```example
+/// $ H stretch(=)^"define" U + p V $
+/// $ f : X stretch(->>, size: #150%)_"surjective" Y $
+/// $ x stretch(harpoons.ltrb, size: #3em) y
+///     stretch(\[, size: #150%) z $
+/// ```
+#[elem(Mathy)]
+pub struct StretchElem {
+    /// The glyph to stretch.
+    #[required]
+    pub body: Content,
+
+    /// The size to stretch to, relative to the maximum size of the glyph and
+    /// its attachments.
+    ///
+    /// This value can be given as a [relative length]($relative), or a
+    /// [function]($function) that receives the size of the glyph as a
+    /// parameter (an absolute length) and should return a (relative) length.
+    /// For example, `{x => x * 80%}` would be equivalent to just specifying `{80%}`.
+    ///
+    /// Note that the sizes of glyphs in math fonts come about in two ways:
+    ///
+    /// - First, there are pre-made variants at specific sizes. This means you
+    ///   will see discrete jumps in the stretched glyph's size as you increase
+    ///   the size parameter. It is up to the font how many pre-made variants
+    ///   there are and what their sizes are.
+    ///
+    /// - Then, if the pre-made variants are all too small, a glyph of the
+    ///   desired size is assembled from parts. The stretched glyph's size will
+    ///   now be the exact size requested.
+    ///
+    /// It could be the case that only one of the above exist for a glyph in
+    /// the font.
+    ///
+    /// The value given here is really a minimum (but if there is no assembly
+    /// for the glyph, this minimum may not be reached), so the actual size of
+    /// the stretched glyph may not match what you specified.
+    ///
+    /// ```example
+    /// #for i in range(0, 15) {
+    ///   $stretch(\[, size: #(10pt + i * 2pt))$
+    /// }
+    ///
+    /// #set math.stretch(size: x => x + 0.5em)
+    /// $x stretch(=)^"def" y$
+    /// ```
+    #[default(Rel::one().into())]
+    pub size: StretchSize,
+}
+
+/// How to size a stretched glyph.
+#[derive(Debug, Clone, PartialEq, Hash)]
+pub enum StretchSize {
+    /// Sized by the specified length.
+    Rel(Rel),
+    /// Resolve the size for the given base size through the specified
+    /// function.
+    Func(Func),
+}
+
+impl StretchSize {
+    /// Resolve the stretch size given the base size.
+    pub fn resolve(
+        &self,
+        engine: &mut Engine,
+        styles: StyleChain,
+        base: Abs,
+    ) -> SourceResult<Abs> {
+        Ok(match self {
+            Self::Rel(rel) => *rel,
+            Self::Func(func) => func
+                .call(engine, Context::new(None, Some(styles)).track(), [base])?
+                .cast()
+                .at(func.span())?,
+        }
+        .resolve(styles)
+        .relative_to(base))
+    }
+
+    /// Whether the size is the default used by `LrElem`.
+    pub fn is_lr_default(self) -> bool {
+        self == <default_lr_size>::data().into()
+    }
+}
+
+impl From<Rel> for StretchSize {
+    fn from(rel: Rel) -> Self {
+        Self::Rel(rel)
+    }
+}
+
+impl From<&'static NativeFuncData> for StretchSize {
+    fn from(data: &'static NativeFuncData) -> Self {
+        Self::Func(Func::from(data))
+    }
+}
+
+cast! {
+    StretchSize,
+    self => match self {
+        Self::Rel(v) => v.into_value(),
+        Self::Func(v) => v.into_value(),
+    },
+    v: Rel => Self::Rel(v),
+    v: Func => Self::Func(v),
+}

crates/typst-library/src/text/font/mod.rs

@@ -228,6 +228,10 @@ pub struct FontMetrics {
     pub underline: LineMetrics,
     /// Recommended metrics for an overline.
     pub overline: LineMetrics,
+    /// Metrics for subscripts, if provided by the font.
+    pub subscript: Option<ScriptMetrics>,
+    /// Metrics for superscripts, if provided by the font.
+    pub superscript: Option<ScriptMetrics>,
 }
 
 impl FontMetrics {
@@ -240,6 +244,7 @@ impl FontMetrics {
         let cap_height = ttf.capital_height().filter(|&h| h > 0).map_or(ascender, to_em);
         let x_height = ttf.x_height().filter(|&h| h > 0).map_or(ascender, to_em);
         let descender = to_em(ttf.typographic_descender().unwrap_or(ttf.descender()));
+
         let strikeout = ttf.strikeout_metrics();
         let underline = ttf.underline_metrics();
 
@@ -262,6 +267,20 @@ impl FontMetrics {
             thickness: underline.thickness,
         };
 
+        let subscript = ttf.subscript_metrics().map(|metrics| ScriptMetrics {
+            width: to_em(metrics.x_size),
+            height: to_em(metrics.y_size),
+            horizontal_offset: to_em(metrics.x_offset),
+            vertical_offset: -to_em(metrics.y_offset),
+        });
+
+        let superscript = ttf.superscript_metrics().map(|metrics| ScriptMetrics {
+            width: to_em(metrics.x_size),
+            height: to_em(metrics.y_size),
+            horizontal_offset: to_em(metrics.x_offset),
+            vertical_offset: to_em(metrics.y_offset),
+        });
+
         Self {
             units_per_em,
             ascender,
@@ -271,6 +290,8 @@ impl FontMetrics {
             strikethrough,
             underline,
             overline,
+            superscript,
+            subscript,
         }
     }
 
@@ -296,6 +317,24 @@ pub struct LineMetrics {
     pub thickness: Em,
 }
 
+/// Metrics for subscripts or superscripts.
+#[derive(Debug, Copy, Clone)]
+pub struct ScriptMetrics {
+    /// The width of those scripts, relative to the outer font size.
+    pub width: Em,
+    /// The height of those scripts, relative to the outer font size.
+    pub height: Em,
+    /// The horizontal (to the right) offset of those scripts, relative to the
+    /// outer font size.
+    ///
+    /// This is used for italic correction.
+    pub horizontal_offset: Em,
+    /// The vertical (to the top) offset of those scripts, relative to the outer font size.
+    ///
+    /// For superscripts, this is positive. For subscripts, this is negative.
+    pub vertical_offset: Em,
+}
+
 /// Identifies a vertical metric of a font.
 #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash, Cast)]
 pub enum VerticalFontMetric {

crates/typst-library/src/text/mod.rs

@@ -755,6 +755,12 @@ pub struct TextElem {
     #[internal]
     #[ghost]
     pub smallcaps: Option<Smallcaps>,
+
+    /// The configuration for superscripts or subscripts, if one of them is
+    /// enabled.
+    #[internal]
+    #[ghost]
+    pub shift_settings: Option<ShiftSettings>,
 }
 
 impl TextElem {
@@ -930,7 +936,7 @@ cast! {
 }
 
 /// Resolve a prioritized iterator over the font families.
-pub fn families(styles: StyleChain) -> impl Iterator<Item = &FontFamily> + Clone {
+pub fn families(styles: StyleChain<'_>) -> impl Iterator<Item = &'_ FontFamily> + Clone {
     let fallbacks = singleton!(Vec<FontFamily>, {
         [
             "libertinus serif",

crates/typst-library/src/text/shift.rs

@@ -1,14 +1,13 @@
-use ecow::EcoString;
-
 use crate::diag::SourceResult;
 use crate::engine::Engine;
 use crate::foundations::{
-    elem, Content, NativeElement, Packed, SequenceElem, Show, StyleChain, TargetElem,
+    elem, Content, NativeElement, Packed, Show, Smart, StyleChain, TargetElem,
 };
 use crate::html::{tag, HtmlElem};
 use crate::layout::{Em, Length};
-use crate::text::{variant, SpaceElem, TextElem, TextSize};
-use crate::World;
+use crate::text::{FontMetrics, TextElem, TextSize};
+use ttf_parser::Tag;
+use typst_library::text::ScriptMetrics;
 
 /// Renders text in subscript.
 ///
@@ -20,11 +19,16 @@ use crate::World;
 /// ```
 #[elem(title = "Subscript", Show)]
 pub struct SubElem {
-    /// Whether to prefer the dedicated subscript characters of the font.
+    /// Whether to create artificial subscripts by lowering and scaling down
+    /// regular glyphs.
     ///
-    /// If this is enabled, Typst first tries to transform the text to subscript
-    /// codepoints. If that fails, it falls back to rendering lowered and shrunk
-    /// normal letters.
+    /// Ideally, subscripts glyphs are provided by the font (using the `subs`
+    /// OpenType feature). Otherwise, Typst is able to synthesize subscripts.
+    ///
+    /// When this is set to `{false}`, synthesized glyphs will be used
+    /// regardless of whether the font provides dedicated subscript glyphs. When
+    /// `{true}`, synthesized glyphs may still be used in case the font does not
+    /// provide the necessary subscript glyphs.
     ///
     /// ```example
     /// N#sub(typographic: true)[1]
@@ -33,17 +37,27 @@ pub struct SubElem {
     #[default(true)]
     pub typographic: bool,
 
-    /// The baseline shift for synthetic subscripts. Does not apply if
-    /// `typographic` is true and the font has subscript codepoints for the
-    /// given `body`.
-    #[default(Em::new(0.2).into())]
-    pub baseline: Length,
+    /// The downward baseline shift for synthesized subscripts.
+    ///
+    /// This only applies to synthesized subscripts. In other words, this has no
+    /// effect if `typographic` is `{true}` and the font provides the necessary
+    /// subscript glyphs.
+    ///
+    /// If set to `{auto}`, the baseline is shifted according to the metrics
+    /// provided by the font, with a fallback to `{0.2em}` in case the font does
+    /// not define the necessary metrics.
+    pub baseline: Smart<Length>,
 
-    /// The font size for synthetic subscripts. Does not apply if
-    /// `typographic` is true and the font has subscript codepoints for the
-    /// given `body`.
-    #[default(TextSize(Em::new(0.6).into()))]
-    pub size: TextSize,
+    /// The font size for synthesized subscripts.
+    ///
+    /// This only applies to synthesized subscripts. In other words, this has no
+    /// effect if `typographic` is `{true}` and the font provides the necessary
+    /// subscript glyphs.
+    ///
+    /// If set to `{auto}`, the size is scaled according to the metrics provided
+    /// by the font, with a fallback to `{0.6em}` in case the font does not
+    /// define the necessary metrics.
+    pub size: Smart<TextSize>,
 
     /// The text to display in subscript.
     #[required]
@@ -52,7 +66,7 @@ pub struct SubElem {
 
 impl Show for Packed<SubElem> {
     #[typst_macros::time(name = "sub", span = self.span())]
-    fn show(&self, engine: &mut Engine, styles: StyleChain) -> SourceResult<Content> {
+    fn show(&self, _: &mut Engine, styles: StyleChain) -> SourceResult<Content> {
         let body = self.body.clone();
 
         if TargetElem::target_in(styles).is_html() {
@@ -62,17 +76,14 @@ impl Show for Packed<SubElem> {
                 .spanned(self.span()));
         }
 
-        if self.typographic(styles) {
-            if let Some(text) = convert_script(&body, true) {
-                if is_shapable(engine, &text, styles) {
-                    return Ok(TextElem::packed(text));
-                }
-            }
-        };
-
-        Ok(body
-            .styled(TextElem::set_baseline(self.baseline(styles)))
-            .styled(TextElem::set_size(self.size(styles))))
+        show_script(
+            styles,
+            body,
+            self.typographic(styles),
+            self.baseline(styles),
+            self.size(styles),
+            ScriptKind::Sub,
+        )
     }
 }
 
@@ -86,11 +97,16 @@ impl Show for Packed<SubElem> {
 /// ```
 #[elem(title = "Superscript", Show)]
 pub struct SuperElem {
-    /// Whether to prefer the dedicated superscript characters of the font.
+    /// Whether to create artificial superscripts by raising and scaling down
+    /// regular glyphs.
     ///
-    /// If this is enabled, Typst first tries to transform the text to
-    /// superscript codepoints. If that fails, it falls back to rendering
-    /// raised and shrunk normal letters.
+    /// Ideally, superscripts glyphs are provided by the font (using the `sups`
+    /// OpenType feature). Otherwise, Typst is able to synthesize superscripts.
+    ///
+    /// When this is set to `{false}`, synthesized glyphs will be used
+    /// regardless of whether the font provides dedicated superscript glyphs.
+    /// When `{true}`, synthesized glyphs may still be used in case the font
+    /// does not provide the necessary superscript glyphs.
     ///
     /// ```example
     /// N#super(typographic: true)[1]
@@ -99,17 +115,31 @@ pub struct SuperElem {
     #[default(true)]
     pub typographic: bool,
 
-    /// The baseline shift for synthetic superscripts. Does not apply if
-    /// `typographic` is true and the font has superscript codepoints for the
-    /// given `body`.
-    #[default(Em::new(-0.5).into())]
-    pub baseline: Length,
+    /// The downward baseline shift for synthesized superscripts.
+    ///
+    /// This only applies to synthesized superscripts. In other words, this has
+    /// no effect if `typographic` is `{true}` and the font provides the
+    /// necessary superscript glyphs.
+    ///
+    /// If set to `{auto}`, the baseline is shifted according to the metrics
+    /// provided by the font, with a fallback to `{-0.5em}` in case the font
+    /// does not define the necessary metrics.
+    ///
+    /// Note that, since the baseline shift is applied downward, you will need
+    /// to provide a negative value for the content to appear as raised above
+    /// the normal baseline.
+    pub baseline: Smart<Length>,
 
-    /// The font size for synthetic superscripts. Does not apply if
-    /// `typographic` is true and the font has superscript codepoints for the
-    /// given `body`.
-    #[default(TextSize(Em::new(0.6).into()))]
-    pub size: TextSize,
+    /// The font size for synthesized superscripts.
+    ///
+    /// This only applies to synthesized superscripts. In other words, this has
+    /// no effect if `typographic` is `{true}` and the font provides the
+    /// necessary superscript glyphs.
+    ///
+    /// If set to `{auto}`, the size is scaled according to the metrics provided
+    /// by the font, with a fallback to `{0.6em}` in case the font does not
+    /// define the necessary metrics.
+    pub size: Smart<TextSize>,
 
     /// The text to display in superscript.
     #[required]
@@ -118,7 +148,7 @@ pub struct SuperElem {
 
 impl Show for Packed<SuperElem> {
     #[typst_macros::time(name = "super", span = self.span())]
-    fn show(&self, engine: &mut Engine, styles: StyleChain) -> SourceResult<Content> {
+    fn show(&self, _: &mut Engine, styles: StyleChain) -> SourceResult<Content> {
         let body = self.body.clone();
 
         if TargetElem::target_in(styles).is_html() {
@@ -128,104 +158,102 @@ impl Show for Packed<SuperElem> {
                 .spanned(self.span()));
         }
 
-        if self.typographic(styles) {
-            if let Some(text) = convert_script(&body, false) {
-                if is_shapable(engine, &text, styles) {
-                    return Ok(TextElem::packed(text));
-                }
-            }
-        };
-
-        Ok(body
-            .styled(TextElem::set_baseline(self.baseline(styles)))
-            .styled(TextElem::set_size(self.size(styles))))
+        show_script(
+            styles,
+            body,
+            self.typographic(styles),
+            self.baseline(styles),
+            self.size(styles),
+            ScriptKind::Super,
+        )
     }
 }
 
-/// Find and transform the text contained in `content` to the given script kind
-/// if and only if it only consists of `Text`, `Space`, and `Empty` leaves.
-fn convert_script(content: &Content, sub: bool) -> Option<EcoString> {
-    if content.is::<SpaceElem>() {
-        Some(' '.into())
-    } else if let Some(elem) = content.to_packed::<TextElem>() {
-        if sub {
-            elem.text.chars().map(to_subscript_codepoint).collect()
-        } else {
-            elem.text.chars().map(to_superscript_codepoint).collect()
-        }
-    } else if let Some(sequence) = content.to_packed::<SequenceElem>() {
-        sequence
-            .children
-            .iter()
-            .map(|item| convert_script(item, sub))
-            .collect()
-    } else {
-        None
-    }
+fn show_script(
+    styles: StyleChain,
+    body: Content,
+    typographic: bool,
+    baseline: Smart<Length>,
+    size: Smart<TextSize>,
+    kind: ScriptKind,
+) -> SourceResult<Content> {
+    let font_size = TextElem::size_in(styles);
+    Ok(body.styled(TextElem::set_shift_settings(Some(ShiftSettings {
+        typographic,
+        shift: baseline.map(|l| -Em::from_length(l, font_size)),
+        size: size.map(|t| Em::from_length(t.0, font_size)),
+        kind,
+    }))))
 }
 
-/// Checks whether the first retrievable family contains all code points of the
-/// given string.
-fn is_shapable(engine: &Engine, text: &str, styles: StyleChain) -> bool {
-    let world = engine.world;
-    for family in TextElem::font_in(styles) {
-        if let Some(font) = world
-            .book()
-            .select(family.as_str(), variant(styles))
-            .and_then(|id| world.font(id))
-        {
-            let covers = family.covers();
-            return text.chars().all(|c| {
-                covers.is_none_or(|cov| cov.is_match(c.encode_utf8(&mut [0; 4])))
-                    && font.ttf().glyph_index(c).is_some()
-            });
+/// Configuration values for sub- or superscript text.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
+pub struct ShiftSettings {
+    /// Whether the OpenType feature should be used if possible.
+    pub typographic: bool,
+    /// The baseline shift of the script, relative to the outer text size.
+    ///
+    /// For superscripts, this is positive. For subscripts, this is negative. A
+    /// value of [`Smart::Auto`] indicates that the value should be obtained
+    /// from font metrics.
+    pub shift: Smart<Em>,
+    /// The size of the script, relative to the outer text size.
+    ///
+    /// A value of [`Smart::Auto`] indicates that the value should be obtained
+    /// from font metrics.
+    pub size: Smart<Em>,
+    /// The kind of script (either a subscript, or a superscript).
+    ///
+    /// This is used to know which OpenType table to use to resolve
+    /// [`Smart::Auto`] values.
+    pub kind: ScriptKind,
+}
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
+pub enum ScriptKind {
+    Sub,
+    Super,
+}
+
+impl ScriptKind {
+    /// Returns the default metrics for this script kind.
+    ///
+    /// This can be used as a last resort if neither the user nor the font
+    /// provided those metrics.
+    pub fn default_metrics(self) -> &'static ScriptMetrics {
+        match self {
+            Self::Sub => &DEFAULT_SUBSCRIPT_METRICS,
+            Self::Super => &DEFAULT_SUPERSCRIPT_METRICS,
         }
     }
 
-    false
-}
+    /// Reads the script metrics from the font table for to this script kind.
+    pub fn read_metrics(self, font_metrics: &FontMetrics) -> &ScriptMetrics {
+        match self {
+            Self::Sub => font_metrics.subscript.as_ref(),
+            Self::Super => font_metrics.superscript.as_ref(),
+        }
+        .unwrap_or(self.default_metrics())
+    }
 
-/// Convert a character to its corresponding Unicode superscript.
-fn to_superscript_codepoint(c: char) -> Option<char> {
-    match c {
-        '1' => Some('¹'),
-        '2' => Some('²'),
-        '3' => Some('³'),
-        '0' | '4'..='9' => char::from_u32(c as u32 - '0' as u32 + '⁰' as u32),
-        '+' => Some('⁺'),
-        '−' => Some('⁻'),
-        '=' => Some('⁼'),
-        '(' => Some('⁽'),
-        ')' => Some('⁾'),
-        'n' => Some('ⁿ'),
-        'i' => Some('ⁱ'),
-        ' ' => Some(' '),
-        _ => None,
+    /// The corresponding OpenType feature.
+    pub const fn feature(self) -> Tag {
+        match self {
+            Self::Sub => Tag::from_bytes(b"subs"),
+            Self::Super => Tag::from_bytes(b"sups"),
+        }
     }
 }
+static DEFAULT_SUBSCRIPT_METRICS: ScriptMetrics = ScriptMetrics {
+    width: Em::new(0.6),
+    height: Em::new(0.6),
+    horizontal_offset: Em::zero(),
+    vertical_offset: Em::new(-0.2),
+};
 
-/// Convert a character to its corresponding Unicode subscript.
-fn to_subscript_codepoint(c: char) -> Option<char> {
-    match c {
-        '0'..='9' => char::from_u32(c as u32 - '0' as u32 + '₀' as u32),
-        '+' => Some('₊'),
-        '−' => Some('₋'),
-        '=' => Some('₌'),
-        '(' => Some('₍'),
-        ')' => Some('₎'),
-        'a' => Some('ₐ'),
-        'e' => Some('ₑ'),
-        'o' => Some('ₒ'),
-        'x' => Some('ₓ'),
-        'h' => Some('ₕ'),
-        'k' => Some('ₖ'),
-        'l' => Some('ₗ'),
-        'm' => Some('ₘ'),
-        'n' => Some('ₙ'),
-        'p' => Some('ₚ'),
-        's' => Some('ₛ'),
-        't' => Some('ₜ'),
-        ' ' => Some(' '),
-        _ => None,
-    }
-}
+static DEFAULT_SUPERSCRIPT_METRICS: ScriptMetrics = ScriptMetrics {
+    width: Em::new(0.6),
+    height: Em::new(0.6),
+    horizontal_offset: Em::zero(),
+    vertical_offset: Em::new(0.5),
+};

crates/typst-pdf/src/metadata.rs

@@ -22,8 +22,6 @@ pub(crate) fn build_metadata(gc: &GlobalContext) -> Metadata {
         .keywords(gc.document.info.keywords.iter().map(EcoString::to_string).collect())
         .authors(gc.document.info.author.iter().map(EcoString::to_string).collect());
 
-    let lang = gc.languages.iter().max_by_key(|(_, &count)| count).map(|(&l, _)| l);
-
     if let Some(lang) = lang {
         metadata = metadata.language(lang.as_str().to_string());
     }

crates/typst-utils/src/lib.rs

@@ -395,6 +395,10 @@ pub fn default_math_class(c: char) -> Option<MathClass> {
         // https://github.com/typst/typst/issues/5764
         '⟇' => Some(MathClass::Binary),
 
+        // Arabic comma.
+        // https://github.com/latex3/unicode-math/pull/633#issuecomment-2028936135
+        '،' => Some(MathClass::Punctuation),
+
         c => unicode_math_class::class(c),
     }
 }

tests/suite/math/accent.typ

@@ -30,11 +30,17 @@ $ tilde(integral), tilde(integral)_a^b, tilde(integral_a^b) $
 
 --- math-accent-sized ---
 // Test accent size.
-$tilde(sum), tilde(sum, size: #50%), accent(H, hat, size: #200%)$
+$tilde(sum), tilde(sum, size: #25%), accent(H, hat, size: #125%)$
 
 --- math-accent-sized-script ---
 // Test accent size in script size.
-$tilde(U, size: #1.1em), x^tilde(U, size: #1.1em), sscript(tilde(U, size: #1.1em))$
+$tilde(U, size: #0.6em), x^tilde(U, size: #0.6em), sscript(tilde(U, size: #0.6em))$
+
+--- math-accent-sized-function ---
+// Test accent size with a function.
+$dash(A) arrow(I) hat(L)$ \
+#set math.accent(size: x => x - 0.1em)
+$dash(A) arrow(I) hat(L)$
 
 --- math-accent-dotless ---
 // Test dotless glyph variants.
@@ -85,7 +91,7 @@ $ accent(integral, \u{20EC}), accent(integral, \u{20EC})_a^b, accent(integral_a^
 
 --- math-accent-bottom-sized ---
 // Test bottom accent size.
-$accent(sum, \u{0330}), accent(sum, \u{0330}, size: #50%), accent(H, \u{032D}, size: #200%)$
+$accent(sum, \u{0330}), accent(sum, \u{0330}, size: #25%), accent(H, \u{032D}, size: #125%)$
 
 --- math-accent-nested ---
 // Test nested top and bottom accents.

tests/suite/math/attach.typ

@@ -187,5 +187,5 @@ $ a0 + a1 + a0_2 \
 --- math-attach-scripts-extended-shapes ---
 // Test script attachments positioning if the base is an extended shape (or a
 // sequence of extended shapes).
-$lr(size: #130%, [x])_0^1, [x]_0^1, \]_0^1, x_0^1, A_0^1$ \
+$lr(size: #115%, [x])_0^1, [x]_0^1, \]_0^1, x_0^1, A_0^1$ \
 $n^2, (n + 1)^2, sum_0^1, integral_0^1$

tests/suite/math/cases.typ

@@ -16,6 +16,12 @@ $ x = cases(1, 2) $
 #set math.cases(delim: sym.angle.l)
 $ cases(a, b, c) $
 
+--- math-cases-delim-size ---
+// Test setting delimiter size.
+$ cases(reverse: #true, 1, 2, 3) cases(delim-size: #100%, 1, 2, 3) $
+#set math.cases(delim-size: x => calc.max(x - 5pt, x * 0.901))
+$ cases(1, 2) cases(1, 2, 3, 4) $
+
 --- math-cases-linebreaks ---
 // Warning: 40-49 linebreaks are ignored in branches
 // Hint: 40-49 use commas instead to separate each line

tests/suite/math/delimited.typ

@@ -31,9 +31,14 @@ $ lr(a/b\]) = a = lr(\{a/b) $
 
 --- math-lr-size ---
 // Test manual scaling.
-$ lr(]sum_(x=1)^n x], size: #70%)
+$ lr(]sum_(x=1)^n x], size: #60%)
   < lr((1, 2), size: #200%) $
 
+--- math-lr-size-function ---
+// Test using a function as an argument to size.
+#set math.lr(size: x => if x > 10pt { 1em } else { 4 * x })
+$ (a) (1/2) $
+
 --- math-lr-shorthands ---
 // Test predefined delimiter pairings.
 $floor(x/2), ceil(x/2), abs(x), norm(x)$
@@ -57,16 +62,16 @@ $ { x mid(|) sum_(i=1)^oo phi_i (x) < 1 } \
 #set page(width: auto)
 
 $ lr({ A mid(|) integral }) quad
-  lr(size: #1em, { A mid(|) integral }) quad
-  lr(size: #(1em+20%), { A mid(|) integral }) \
+  lr(size: #0%, { A mid(|) integral }) quad
+  lr(size: #(1em+10%), { A mid(|) integral }) \
 
   lr(] A mid(|) integral ]) quad
-  lr(size: #1em, ] A mid(|) integral ]) quad
-  lr(size: #(1em+20%), ] A mid(|) integral ]) \
+  lr(size: #0%, ] A mid(|) integral ]) quad
+  lr(size: #(1em+10%), ] A mid(|) integral ]) \
 
   lr(( A mid(|) integral ]) quad
-  lr(size: #1em, ( A mid(|) integral ]) quad
-  lr(size: #(1em+20%), ( A mid(|) integral ]) $
+  lr(size: #0%, ( A mid(|) integral ]) quad
+  lr(size: #(1em+10%), ( A mid(|) integral ]) $
 
 --- math-lr-mid-size-nested-equation ---
 // Test mid size when lr size is set, when nested in an equation.
@@ -74,8 +79,8 @@ $ lr({ A mid(|) integral }) quad
 
 #let body = ${ A mid(|) integral }$
 $ lr(body) quad
-  lr(size: #1em, body) quad
-  lr(size: #(1em+20%), body) $
+  lr(size: #0%, body) quad
+  lr(size: #(1em+10%), body) $
 
 --- math-lr-mid-class ---
 // Test that `mid` creates a Relation, but that can be overridden.

tests/suite/math/mat.typ

@@ -54,6 +54,12 @@ $ a + mat(delim: #none, 1, 2; 3, 4) + b $
   $ mat(1, 2; 3, 4; delim: "[") $,
 )
 
+--- math-mat-delim-size ---
+// Test setting delimiter size.
+$ mat(c; c; c) mat(delim-size: #100%, c; c; c) $
+#set math.mat(delim-size: x => calc.max(x - 5pt, x * 0.901))
+$ mat(delim: "[", f; f; f; f) mat(delim: ||, x; x; x; x) $
+
 --- math-mat-spread ---
 // Test argument spreading in matrix.
 $ mat(..#range(1, 5).chunks(2))

tests/suite/math/stretch.typ

@@ -91,3 +91,9 @@ $ body^"text" $
   }
   $body^"long text"$
 }
+
+--- math-stretch-function ---
+// Test using a function as an argument to size.
+$stretch(<-, size: #(x => x - 0.5em))_"function"$
+#set math.stretch(size: x => x + 0.5em)
+$stretch(|) |$

tests/suite/math/vec.typ

@@ -50,6 +50,12 @@ $ vec(1, 2) $
 // Error: 22-33 invalid delimiter: "%"
 #set math.vec(delim: (none, "%"))
 
+--- math-vec-delim-size ---
+// Test setting delimiter size.
+$ vec(1, 2, 3) vec(delim-size: #100%, 1, 2, 3) $
+#set math.vec(delim-size: x => calc.max(x - 5pt, x * 0.901))
+$ vec(delim: "{", 1, 2, 3) vec(delim: "[", 1, 2, 3) $
+
 --- math-vec-linebreaks ---
 // Warning: 20-29 linebreaks are ignored in elements
 // Hint: 20-29 use commas instead to separate each line

tests/suite/text/shift.typ

@@ -1,22 +1,89 @@
 // Test sub- and superscript shifts.
 
 --- sub-super ---
+#let sq = box(square(size: 4pt))
 #table(
   columns: 3,
-  [Typo.], [Fallb.], [Synth],
-  [x#super[1]], [x#super[5n]], [x#super[2 #box(square(size: 6pt))]],
-  [x#sub[1]], [x#sub[5n]], [x#sub[2 #box(square(size: 6pt))]],
+  [Typo.], [Fallb.], [Synth.],
+  [x#super[1#sq]], [x#super[5: #sq]], [x#super(typographic: false)[2 #sq]],
+  [x#sub[1#sq]], [x#sub[5: #sq]], [x#sub(typographic: false)[2 #sq]],
 )
 
+--- sub-super-typographic ---
+#set text(size: 20pt)
+// Libertinus Serif supports "subs" and "sups" for `typo` and `sq`, but not for
+// `synth`.
+#let synth = [1,2,3]
+#let typo = [123]
+#let sq = [1#box(square(size: 4pt))2]
+x#super(synth) x#super(typo) x#super(sq) \
+x#sub(synth) x#sub(typo) x#sub(sq)
+
+--- sub-super-italic-compensation ---
+#set text(size: 20pt, style: "italic")
+// Libertinus Serif supports "subs" and "sups" for `typo`, but not for `synth`.
+#let synth = [1,2,3]
+#let typo = [123]
+#let sq = [1#box(square(size: 4pt))2]
+x#super(synth) x#super(typo) x#super(sq) \
+x#sub(synth) x#sub(typo) x#sub(sq)
+
 --- sub-super-non-typographic ---
 #set super(typographic: false, baseline: -0.25em, size: 0.7em)
 n#super[1], n#sub[2], ... n#super[N]
 
 --- super-underline ---
 #set underline(stroke: 0.5pt, offset: 0.15em)
-#underline[The claim#super[\[4\]]] has been disputed. \
-The claim#super[#underline[\[4\]]] has been disputed. \
-It really has been#super(box(text(baseline: 0pt, underline[\[4\]]))) \
+#set super(typographic: false)
+#underline[A#super[4]] B \
+A#super[#underline[4]] B \
+A #underline(super[4]) B \
+#set super(typographic: true)
+#underline[A#super[4]] B \
+A#super[#underline[4]] B \
+A #underline(super[4]) B
+
+--- super-highlight ---
+#set super(typographic: false)
+#highlight[A#super[4]] B \
+A#super[#highlight[4]] B \
+A#super(highlight[4]) \
+#set super(typographic: true)
+#highlight[A#super[4]] B \
+A#super[#highlight[4]] B \
+A#super(highlight[4])
+
+--- super-1em ---
+#set text(size: 10pt)
+#super(context test(1em.to-absolute(), 10pt))
+
+--- long-scripts ---
+|longscript| \
+|#super(typographic: true)[longscript]| \
+|#super(typographic: false)[longscript]| \
+|#sub(typographic: true)[longscript]| \
+|#sub(typographic: false)[longscript]|
+
+--- script-metrics-bundeled-fonts ---
+// Tests whether the script metrics are used properly by synthesizing
+// superscripts and subscripts for all bundled fonts.
+
+#set super(typographic: false)
+#set sub(typographic: false)
+
+#let test(font, weights, styles) = {
+  for weight in weights {
+    for style in styles {
+      text(font: font, weight: weight, style: style)[Xx#super[Xx]#sub[Xx]]
+      linebreak()
+    }
+  }
+}
+
+#test("DejaVu Sans Mono", ("regular", "bold"), ("normal", "oblique"))
+#test("Libertinus Serif", ("regular", "semibold", "bold"), ("normal", "italic"))
+#test("New Computer Modern", ("regular", "bold"), ("normal", "italic"))
+#test("New Computer Modern Math", (400, 450, "bold"), ("normal",))
 
 --- basic-sup-sub html ---
 1#super[st], 2#super[nd], 3#super[rd].