Make note of forks that can be optimized
diff --git a/src/data.rs b/src/data.rs
index f54f5b9..d616832 100644
--- a/src/data.rs
+++ b/src/data.rs
@@ -268,6 +268,7 @@
             let pub_token = input.parse::<Token![pub]>()?;
 
             if input.peek(token::Paren) {
+                // TODO: optimize using advance_to
                 let ahead = input.fork();
                 let mut content;
                 parenthesized!(content in ahead);