diff --git a/script/src/lib.rs b/script/src/lib.rs
index 5adfd1fc9c..8b2d128039 100644
--- a/script/src/lib.rs
+++ b/script/src/lib.rs
@@ -9,8 +9,8 @@ mod verify_env;
 
 pub use crate::error::{ScriptError, TransactionScriptError};
 pub use crate::types::{
-    CoreMachine, ScriptGroup, ScriptGroupType, ScriptVersion, TransactionSnapshot,
-    TransactionState, VerifyResult, VmIsa, VmVersion,
+    CoreMachine, MachineContext, ResumableMachine, ScriptGroup, ScriptGroupType, ScriptVersion,
+    TransactionSnapshot, TransactionState, VerifyResult, VmIsa, VmVersion,
 };
 pub use crate::verify::{TransactionScriptsSyscallsGenerator, TransactionScriptsVerifier};
 pub use crate::verify_env::TxVerifyEnv;
diff --git a/script/src/types.rs b/script/src/types.rs
index 055c3c0f7e..1fdab303c1 100644
--- a/script/src/types.rs
+++ b/script/src/types.rs
@@ -117,7 +117,8 @@ pub(crate) type Machine = TraceMachine<CoreMachine>;
 /// a chain of spawned machines.
 #[derive(Default)]
 pub struct MachineContext {
-    pub(crate) suspended_machines: Vec<ResumableMachine>,
+    /// A stack of ResumableMachines.
+    pub suspended_machines: Vec<ResumableMachine>,
 }
 
 /// Data structure captured all environment data for a suspended machine
@@ -175,8 +176,11 @@ impl TryFrom<&SpawnData> for ResumePoint {
     }
 }
 
+/// An enumerated type indicating the type of the Machine.
 pub enum ResumableMachine {
+    /// Root machine instance.
     Initial(Machine),
+    /// A machine which created by spawn syscall.
     Spawn(Machine, SpawnData),
 }
 
@@ -211,10 +215,12 @@ impl ResumableMachine {
         set_vm_max_cycles(self.machine_mut(), cycles)
     }
 
+    /// Add cycles to current machine.
     pub fn add_cycles(&mut self, cycles: Cycle) -> Result<(), VMInternalError> {
         self.machine_mut().machine.add_cycles(cycles)
     }
 
+    /// Run machine.
     pub fn run(&mut self) -> Result<i8, VMInternalError> {
         self.machine_mut().run()
     }