Forms: doc comments for the functions this change touches

crates/ui-egui/src/canvas.rs

@@ -2365,6 +2365,8 @@ fn page_scroll<R>(
     ui.scope_builder(egui::UiBuilder::new().id(id), |ui| scroll.show_viewport(ui, draw)).inner
 }
 
+/// Draws the document tab at `index`: its notice bars, then its pages (or the Organize grid) in a
+/// scroll area with this frame's zoom, scrolling, tool input, overlays and render requests.
 pub fn document_area(app: &mut PdfCraftApp, index: usize, ui: &mut egui::Ui) {
     let t = Tokens::get(ui.ctx());
     // Keyboard scrolling applies to this frame's page view only, never later.