Fix plain list item.

src/wasm/plain_list_item.rs

@@ -42,7 +42,15 @@ to_wasm!(
         Ok((
             children,
             WasmPlainListItem {
-                tag: Vec::new(),
+                tag: original
+                    .tag
+                    .iter()
+                    .map(|child| {
+                        child
+                            .to_wasm(wasm_context.clone())
+                            .map(Into::<WasmAstNode>::into)
+                    })
+                    .collect::<Result<Vec<_>, _>>()?,
                 bullet: original.bullet.to_owned(),
                 counter: original.counter.clone(),
                 checkbox: original.checkbox.as_ref().map(|(checkbox_type, _)| {