Function structure 

pub fn structure(path: &str, source: &str, blocks: Vec<Block>) -> Doc

Groups blocks (scanned from source) into a Doc.

This is pure syntax — it does NOT decide where one example ends and the next begins. Instead each candidate records preceded_by_delimiter (a heading or --- sits before it), and the planner groups adjacent matching candidates into examples using that flag plus which candidates match a step. See ADR 0012.