diff --git a/androscalpel/src/instructions.rs b/androscalpel/src/instructions.rs
index a341235..dc85dfb 100644
--- a/androscalpel/src/instructions.rs
+++ b/androscalpel/src/instructions.rs
@@ -101,10 +101,21 @@ pub enum Instruction {
     CheckCast { reg: u8, lit: IdType },
     /// Check if an object if an instance of a type.
     /// (put 1 in the dest register if yes, else 0)
-    InstanceOf { dest: u8, obj: u8, lit: IdType },
+    InstanceOf {
+        /// 4 bit register
+        dest: u8,
+        /// 4 bit register
+        obj: u8,
+        lit: IdType,
+    },
     /// Get the number of item in an array.
     /// (put the lenght in the dest register)
-    ArrayLength { dest: u8, arr: u8 },
+    ArrayLength {
+        /// 4 bit register
+        dest: u8,
+        /// 4 bit register
+        arr: u8,
+    },
     /// Construct a new instance of the indicated type and store a reference to it.
     NewInstance { reg: u8, lit: IdType },
     /// Construct a new array of the indicated type and size in size_reg and store a reference to it.