Function dump_tree 

pub fn dump_tree<R: Resolve>(
    tree: Option<&StructTree>,
    page_index: impl Into<PageIndex>,
    r: &R,
) -> String

Renders one page’s structure tree.

A document with no tree contributes nothing at all — not even a header — which is why most of the corpus’s structure goldens are empty files. A tree that loaded but reached no elements still prints its header and the two trailing blank lines.