Function collect_fragments 

pub fn collect_fragments(
    plan: &PagePlan,
    parser: &dyn SourceParser,
    entry_markup: Option<&str>,
) -> Result<FragmentTable, String>

Merge the fragments every one of the app’s .lmn files declares into the one table each page parses against. This is what makes a <template> in layout.lmn reachable from every page.

Two files declaring the same name with different bodies is an error: the table is app-wide, so either answer would silently change what half the use sites render.