diff --git a/pyscroll/animation.py b/pyscroll/animation.py
index 504d1ab..a955cfc 100644
--- a/pyscroll/animation.py
+++ b/pyscroll/animation.py
@@ -1,19 +1,30 @@
 from __future__ import annotations
 
-from collections import namedtuple
 from collections.abc import Sequence
-from typing import Union
+from typing import NamedTuple, Union
+
+from pygame import Surface
+
+
+class AnimationFrame(NamedTuple):
+    image: Surface
+    duration: float
+
 
-AnimationFrame = namedtuple("AnimationFrame", "image duration")
 TimeLike = Union[float, int]
 
 __all__ = ("AnimationFrame", "AnimationToken")
 
 
 class AnimationToken:
-    __slots__ = ["next", "positions", "frames", "index"]
-
-    def __init__(self, positions, frames: Sequence, initial_time: int = 0) -> None:
+    __slots__ = ["_next", "positions", "frames", "index"]
+
+    def __init__(
+        self,
+        positions: set[tuple[int, int, int]],
+        frames: Sequence[AnimationFrame],
+        initial_time: float = 0.0,
+    ) -> None:
         """
         Constructor
 
@@ -22,14 +33,19 @@ def __init__(self, positions, frames: Sequence, initial_time: int = 0) -> None:
             frames: Sequence of frames that compromise the animation
             initial_time: Used to compensate time between starting and changing animations
 
+        Raises:
+            ValueError: If the frames sequence is empty
         """
-        frames = tuple(AnimationFrame(*i) for i in frames)
+        if not frames:
+            raise ValueError("Frames sequence cannot be empty")
+
+        frames = tuple(AnimationFrame(*frame_data) for frame_data in frames)
         self.positions = positions
         self.frames = frames
-        self.next = frames[0].duration + initial_time
+        self._next = frames[0].duration + initial_time
         self.index = 0
 
-    def advance(self, last_time: TimeLike):
+    def advance(self, last_time: TimeLike) -> AnimationFrame:
         """
         Advance the frame, and set timer for next frame
 
@@ -43,6 +59,8 @@ def advance(self, last_time: TimeLike):
         Args:
             last_time: Duration of the last frame
 
+        Returns:
+            AnimationFrame: The next frame in the animation
         """
         # advance the animation frame index, looping by default
         if self.index == len(self.frames) - 1:
@@ -52,11 +70,23 @@ def advance(self, last_time: TimeLike):
 
         # set the timer for the next advance
         next_frame = self.frames[self.index]
-        self.next = next_frame.duration + last_time
+        self._next = next_frame.duration + last_time
         return next_frame
 
     def __lt__(self, other):
+        """
+        Compare the animation token with another object based on the next frame time
+
+        Args:
+            other: The object to compare with
+
+        Returns:
+            bool: True if the next frame time is less than the other object's time
+        """
         try:
-            return self.next < other.next
+            return self._next < other._next
         except AttributeError:
-            return self.next < other
+            return self._next < other
+
+    def __repr__(self) -> str:
+        return f"AnimationToken(positions={self.positions}, frames={self.frames})"