diff --git a/src/util/mod.rs b/src/util/mod.rs
index 94df1a4..06b69f8 100644
--- a/src/util/mod.rs
+++ b/src/util/mod.rs
@@ -282,16 +282,28 @@ impl<T> Freeze<T> for T {
     }
 }
 
+/// A type containing listeners of this event,
+/// which can be invoked by an invoker.
+///
+/// The listeners are sorted by phases ([`i8`] by default)
+/// that can be called by order.
+///
+/// This type was inspired by the event system in Fabric API.
 pub struct Event<T, Phase = i8>
 where
     T: ?Sized + 'static,
     Phase: Ord,
 {
-    listeners_and_cache:
-        parking_lot::RwLock<(Vec<(Phase, *const T)>, Option<Box<T>>, Vec<&'static T>)>,
+    /// Whether listeners has been modified before requesting the invoker.
+    dirty: std::sync::atomic::AtomicBool,
+
     invoker_factory: fn(&'static [&'static T]) -> Box<T>,
 
-    dirty: std::sync::atomic::AtomicBool,
+    /// 0: raw listeners with phases
+    /// 1: cached invoker
+    /// 2: cached listener references
+    listeners_and_cache:
+        parking_lot::RwLock<(Vec<(Phase, *const T)>, Option<Box<T>>, Vec<&'static T>)>,
 }
 
 impl<T, Phase> Event<T, Phase>
@@ -299,6 +311,13 @@ where
     T: ?Sized,
     Phase: Ord,
 {
+    /// Create a new event with provided event factory.
+    ///
+    /// To avoid lifetime problems in the factory, listeners
+    /// provied are all in static references so that they're
+    /// able to be copied and moved.
+    /// So you should add a `move` keyword before the closure
+    /// to return in the factory.
     pub const fn new(invoker_factory: fn(&'static [&'static T]) -> Box<T>) -> Self {
         Self {
             listeners_and_cache: parking_lot::RwLock::new((Vec::new(), None, Vec::new())),
@@ -307,6 +326,11 @@ where
         }
     }
 
+    /// Get the invoker of this event.
+    ///
+    /// Once the invoker is created, it will be cached until
+    /// the next modification of listeners, and will be re-created
+    /// by the factory.
     pub fn invoker(&self) -> &T {
         if self.dirty.load(std::sync::atomic::Ordering::Acquire) {
             let mut write_guard = self.listeners_and_cache.write();
@@ -328,6 +352,7 @@ where
         unsafe { &*(self.listeners_and_cache.read().1.as_ref().unwrap().deref() as *const T) }
     }
 
+    /// Register a listener to this event for the specified phase.
     pub fn register_with_phase(&mut self, listener: Box<T>, phase: Phase) {
         self.listeners_and_cache
             .get_mut()
@@ -345,6 +370,7 @@ where
     T: ?Sized,
     Phase: Ord + Default,
 {
+    /// Register a listener to this event for the default phase.
     pub fn register(&mut self, listener: Box<T>) {
         self.register_with_phase(listener, Default::default())
     }
@@ -392,15 +418,17 @@ mod event_tests {
                         return false;
                     }
                 }
-
                 true
             })
         });
 
+        assert!(event.invoker()(
+            "minecraft by mojang is a propritary software."
+        ));
+
         event.register(Box::new(|string| {
             !string.to_lowercase().contains("propritary software")
         }));
-
         event.register(Box::new(|string| !string.to_lowercase().contains("mojang")));
         event.register(Box::new(|string| {
             !string.to_lowercase().contains("minecraft")
@@ -416,4 +444,40 @@ mod event_tests {
 
         assert!(!event.invoker()("i love krlite."));
     }
+
+    #[test]
+    fn phases() {
+        let mut event: Event<dyn Fn(&mut String)> = Event::new(|listeners| {
+            Box::new(move |string| {
+                for listener in listeners {
+                    listener(string);
+                }
+            })
+        });
+
+        event.register(Box::new(|string| string.push_str("genshin impact ")));
+        event.register_with_phase(Box::new(|string| string.push_str("you're right, ")), -3);
+        event.register_with_phase(Box::new(|string| string.push_str("but ")), -2);
+        event.register_with_phase(Box::new(|string| string.push_str("is a...")), 10);
+
+        {
+            let mut string = String::new();
+            event.invoker()(&mut string);
+            assert_eq!(string, "you're right, but genshin impact is a...");
+        }
+
+        event.register_with_phase(
+            Box::new(|string| string.push_str("genshin impact, bootstrap! ")),
+            -100,
+        );
+
+        {
+            let mut string = String::new();
+            event.invoker()(&mut string);
+            assert_eq!(
+                string,
+                "genshin impact, bootstrap! you're right, but genshin impact is a..."
+            );
+        }
+    }
 }