feat: mark numbering prefix of heading and outline as Lbl

crates/typst-layout/src/rules.rs

@@ -275,7 +275,7 @@ const HEADING_RULE: ShowFn<HeadingElem> = |elem, engine, styles| {
 
         let spacing = HElem::new(SPACING_TO_NUMBERING.into()).with_weak(true).pack();
 
-        realized = numbering + spacing + realized;
+        realized = PdfMarkerTag::Label(numbering) + spacing + realized;
     }
 
     let block = if indent != Abs::zero() {
@@ -477,7 +477,6 @@ const OUTLINE_ENTRY_RULE: ShowFn<OutlineEntry> = |elem, engine, styles| {
     let context = Context::new(None, Some(styles));
     let context = context.track();
 
-    // TODO(accessibility): prefix should be wrapped in a `Lbl` structure element
     let prefix = elem.prefix(engine, context, span)?;
     let body = elem.body().at(span)?;
     let page = elem.page(engine, context, span)?;

crates/typst-library/src/model/outline.rs

@@ -21,6 +21,7 @@ use crate::layout::{
     RepeatElem, Sides,
 };
 use crate::model::{HeadingElem, NumberingPattern, ParElem, Refable};
+use crate::pdf::PdfMarkerTag;
 use crate::text::{LocalName, SpaceElem, TextElem};
 
 /// A table of contents, figures, or other elements.
@@ -493,7 +494,7 @@ impl OutlineEntry {
         let styles = context.styles().at(span)?;
         let numbers =
             outlinable.counter().display_at_loc(engine, loc, styles, numbering)?;
-        Ok(Some(outlinable.prefix(numbers)))
+        Ok(Some(PdfMarkerTag::Label(outlinable.prefix(numbers))))
     }
 
     /// Creates the default inner content of the entry.

crates/typst-library/src/pdf/accessibility.rs

@@ -138,4 +138,6 @@ pdf_marker_tag! {
     ListItemLabel,
     /// `LBody` of the enum item
     ListItemBody,
+    /// A generic `Lbl`
+    Label,
 }

crates/typst-pdf/src/tags/mod.rs

@@ -69,6 +69,7 @@ pub(crate) fn handle_start(
                 push_stack(gc, loc, StackEntryKind::ListItemBody)?;
                 return Ok(());
             }
+            PdfMarkerTagKind::Label => TagKind::Lbl.into(),
         }
     } else if let Some(entry) = elem.to_packed::<OutlineEntry>() {
         push_stack(gc, loc, StackEntryKind::OutlineEntry(entry.clone()))?;