diff --git a/src/lib.rs b/src/lib.rs
index 4ec8db5144c1b76e3d85bb63d74f1ab7f5917b8b..95cd285f7e0388a6ec79b9902de5ab7e522e46ec 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -105,14 +105,22 @@ impl App {
 /// `$($Ident: $Path,)*`
 pub type Crcs = HashMap<Ident, Path>;
 
+/// Input port binding
+#[derive(Debug)]
 pub enum IpTo {
+    /// Input port connecting to inner Crc
     Crc(Path),
+    /// Input port connecting to method
     Method(Ident),
 }
 
+///
+#[derive(Debug)]
 pub struct Ip {
+    /// Input port type
     ty: Ty,
-    to: IpBind,
+    /// Input port binding
+    to: IpTo,
 }
 
 /// `$($Ident: $Ty,)*`