pub(crate) fn build_nonterminal_map(book: &Book) -> HashMap<String, String>Expand description
Scans all chapters for headings matching ## `Nonterminal` definition
and builds a map from nonterminal name to relative URL for cross-chapter linking.
💡 The heading convention is ## `Function` definition which mdbook generates
as an anchor like #function-definition. For cross-chapter links, we also need
the chapter’s path (e.g., syntax/items.html).