feat: [no ci] pdf.tag function to manually create pdf tags

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

@@ -1,3 +1,4 @@
+use ecow::EcoString;
 use typst_macros::{cast, elem};
 
 use crate::diag::SourceResult;
@@ -6,9 +7,189 @@ use crate::foundations::{Content, Packed, Show, StyleChain};
 use crate::introspection::Locatable;
 
 // TODO: docs
+#[elem(Locatable, Show)]
+pub struct PdfTagElem {
+    #[default(PdfTagKind::NonStruct)]
+    pub kind: PdfTagKind,
+
+    /// An alternate description.
+    pub alt: Option<EcoString>,
+    /// Exact replacement for this structure element and its children.
+    pub actual_text: Option<EcoString>,
+    /// The expanded form of an abbreviation/acronym.
+    pub expansion: Option<EcoString>,
+
+    /// The content to underline.
+    #[required]
+    pub body: Content,
+}
+
+impl Show for Packed<PdfTagElem> {
+    #[typst_macros::time(name = "pdf.tag", span = self.span())]
+    fn show(&self, _: &mut Engine, _: StyleChain) -> SourceResult<Content> {
+        Ok(self.body.clone())
+    }
+}
+
+// TODO: docs
+/// PDF structure elements
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub enum PdfTagKind {
+    // grouping elements
+    /// (Part)
+    Part,
+    /// (Article)
+    Art,
+    /// (Section)
+    Sect,
+    /// (Division)
+    Div,
+    /// (Block quotation)
+    BlockQuote,
+    /// (Caption)
+    Caption,
+    /// (Table of contents)
+    TOC,
+    /// (Table of contents item)
+    TOCI,
+    /// (Index)
+    Index,
+    /// (Nonstructural element)
+    NonStruct,
+    /// (Private element)
+    Private,
+
+    // paragraph like elements
+    /// (Heading)
+    H { title: Option<EcoString> },
+    /// (Heading level 1)
+    H1 { title: Option<EcoString> },
+    /// (Heading level 2)
+    H2 { title: Option<EcoString> },
+    /// (Heading level 3)
+    H4 { title: Option<EcoString> },
+    /// (Heading level 4)
+    H3 { title: Option<EcoString> },
+    /// (Heading level 5)
+    H5 { title: Option<EcoString> },
+    /// (Heading level 6)
+    H6 { title: Option<EcoString> },
+    /// (Paragraph)
+    P,
+
+    // list elements
+    /// (List)
+    L { numbering: ListNumbering },
+    /// (List item)
+    LI,
+    /// (Label)
+    Lbl,
+    /// (List body)
+    LBody,
+
+    // table elements
+    /// (Table)
+    Table,
+    /// (Table row)
+    TR,
+    /// (Table header)
+    TH { scope: TableHeaderScope },
+    /// (Table data cell)
+    TD,
+    /// (Table header row group)
+    THead,
+    /// (Table body row group)
+    TBody,
+    /// (Table footer row group)
+    TFoot,
+
+    // inline elements
+    /// (Span)
+    Span,
+    /// (Quotation)
+    Quote,
+    /// (Note)
+    Note,
+    /// (Reference)
+    Reference,
+    /// (Bibliography Entry)
+    BibEntry,
+    /// (Code)
+    Code,
+    /// (Link)
+    Link,
+    /// (Annotation)
+    Annot,
+
+    /// (Ruby)
+    Ruby,
+    /// (Ruby base text)
+    RB,
+    /// (Ruby annotation text)
+    RT,
+    /// (Ruby punctuation)
+    RP,
+
+    /// (Warichu)
+    Warichu,
+    /// (Warichu text)
+    WT,
+    /// (Warichu punctuation)
+    WP,
+
+    /// (Figure)
+    Figure,
+    /// (Formula)
+    Formula,
+    /// (Form)
+    Form,
+}
+
+cast! {
+    PdfTagKind,
+    self => match self {
+        PdfTagKind::Part => "part".into_value(),
+        _ => todo!(),
+    },
+    "part" => Self::Part,
+    // TODO
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub enum ListNumbering {
+    /// No numbering.
+    None,
+    /// Solid circular bullets.
+    Disc,
+    /// Open circular bullets.
+    Circle,
+    /// Solid square bullets.
+    Square,
+    /// Decimal numbers.
+    Decimal,
+    /// Lowercase Roman numerals.
+    LowerRoman,
+    /// Uppercase Roman numerals.
+    UpperRoman,
+    /// Lowercase letters.
+    LowerAlpha,
+    /// Uppercase letters.
+    UpperAlpha,
+}
+
+/// The scope of a table header cell.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub enum TableHeaderScope {
+    /// The header cell refers to the row.
+    Row,
+    /// The header cell refers to the column.
+    Column,
+    /// The header cell refers to both the row and the column.
+    Both,
+}
 
 /// Mark content as a PDF artifact.
-/// TODO: also use to mark html elements with `aria-hidden="true"`?
+/// TODO: maybe generalize this and use it to mark html elements with `aria-hidden="true"`?
 #[elem(Locatable, Show)]
 pub struct ArtifactElem {
     #[default(ArtifactKind::Other)]

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

@@ -13,6 +13,7 @@ pub fn module() -> Module {
     let mut pdf = Scope::deduplicating();
     pdf.start_category(crate::Category::Pdf);
     pdf.define_elem::<EmbedElem>();
+    pdf.define_elem::<PdfTagElem>();
     pdf.define_elem::<ArtifactElem>();
     Module::new("pdf", pdf)
 }

crates/typst-pdf/src/tags.rs

@@ -12,7 +12,7 @@ use typst_library::model::{
     Destination, FigureCaption, FigureElem, HeadingElem, Outlinable, OutlineElem,
     OutlineEntry,
 };
-use typst_library::pdf::{ArtifactElem, ArtifactKind};
+use typst_library::pdf::{ArtifactElem, ArtifactKind, PdfTagElem, PdfTagKind};
 use typst_library::visualize::ImageElem;
 
 use crate::convert::GlobalContext;
@@ -196,7 +196,13 @@ pub(crate) fn handle_start(
 
     let mut link_id = None;
     let mut wrappers = Vec::new();
-    let tag = if let Some(heading) = elem.to_packed::<HeadingElem>() {
+    let tag = if let Some(pdf_tag) = elem.to_packed::<PdfTagElem>() {
+        let kind = pdf_tag.kind(StyleChain::default());
+        match kind {
+            PdfTagKind::Part => Tag::Part,
+            _ => todo!(),
+        }
+    } else if let Some(heading) = elem.to_packed::<HeadingElem>() {
         let level = heading.level();
         let name = heading.body.plain_text().to_string();
         match level.get() {