Remove unnecessary additional properties in the already-implemented types.

src/wasm/headline.rs

@@ -129,7 +129,7 @@ to_wasm!(
                     })
                     .map_or(Ok(None), |r| r.map(Some))?
                     .map(|child| Box::new(child)),
-                pre_blank: 0,
+                pre_blank: 0, // TODO: Should this be a no-op?
             },
         ))
     }