feat!: Flatten LeafOp

hugr/src/ops/leaf.rs

@@ -13,8 +13,14 @@ use crate::{
     types::{EdgeKind, FunctionType, Type, TypeRow},
 };
 
-/// A user-defined operation that can be downcasted by the extensions that
-/// define it.
+/// A user-defined operation defined in an extension.
+///
+/// Any custom operation can be encoded as a serializable [`OpaqueOp`].
+/// If the operation's extension is loaded in the current context, the operation
+/// can be resolved to an executable [`ExtensionOp`].
+///
+///   [`OpaqueOp`]: crate::ops::custom::OpaqueOp
+///   [`ExtensionOp`]: crate::ops::custom::ExtensionOp
 #[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
 pub struct CustomOp(Box<ExternalOp>);