diff --git a/src/operation_transformation/operation.rs b/src/operation_transformation/operation.rs
index e194f9c..827da77 100644
--- a/src/operation_transformation/operation.rs
+++ b/src/operation_transformation/operation.rs
@@ -15,7 +15,7 @@ use crate::{
 
 /// Represents a change that can be applied on a `StringBuilder`.
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
-#[derive(Clone, PartialEq)]
+#[derive(Clone)]
 pub enum Operation<T>
 where
     T: PartialEq + Clone + std::fmt::Debug,
@@ -42,6 +42,40 @@ where
     },
 }
 
+impl<T> PartialEq for Operation<T>
+where
+    T: PartialEq + Clone + std::fmt::Debug,
+{
+    fn eq(&self, other: &Self) -> bool {
+        match (self, other) {
+            (
+                Operation::Equal { length, .. },
+                Operation::Equal {
+                    length: other_length,
+                    ..
+                },
+            ) => length == other_length,
+            (
+                Operation::Insert { text, .. },
+                Operation::Insert {
+                    text: other_text, ..
+                },
+            ) => text == other_text,
+            (
+                Operation::Delete {
+                    deleted_character_count,
+                    ..
+                },
+                Operation::Delete {
+                    deleted_character_count: other_deleted_character_count,
+                    ..
+                },
+            ) => deleted_character_count == other_deleted_character_count,
+            _ => false,
+        }
+    }
+}
+
 impl<T> Operation<T>
 where
     T: PartialEq + Clone + std::fmt::Debug,
@@ -129,24 +163,28 @@ where
             Operation::Equal {
                 #[cfg(debug_assertions)]
                 text,
+                length,
                 ..
             } => {
                 #[cfg(debug_assertions)]
                 debug_assert!(
                     text.as_ref()
                         .is_none_or(|text| builder.get_slice(self.range()) == *text),
-                    "Text which is supposed to be equal does not match the text in the range"
+                    "Text (`{}`) which is supposed to be equal does not match the text in the \
+                     range: `{}`",
+                    text.as_ref().unwrap_or(&"".to_owned()),
+                    builder.get_slice(self.range())
                 );
 
-                return builder;
+                builder.retain(*length)
+            }
+            Operation::Insert { text, .. } => {
+                builder.insert(&text.iter().map(Token::original).collect::<String>())
             }
-            Operation::Insert { text, .. } => builder.insert(
-                self.start_index(),
-                &text.iter().map(Token::original).collect::<String>(),
-            ),
             Operation::Delete {
                 #[cfg(debug_assertions)]
                 deleted_text,
+                deleted_character_count,
                 ..
             } => {
                 #[cfg(debug_assertions)]
@@ -154,10 +192,12 @@ where
                     deleted_text
                         .as_ref()
                         .is_none_or(|text| builder.get_slice(self.range()) == *text),
-                    "Text to delete does not match the text in the range"
+                    "Text to delete (`{}`) does not match the text in the range: {}",
+                    deleted_text.as_ref().unwrap_or(&"".to_owned()),
+                    builder.get_slice(self.range())
                 );
 
-                builder.delete(self.range());
+                builder.delete(*deleted_character_count)
             }
         }
 
@@ -424,7 +464,7 @@ where
                     f,
                     "<equal {} from index {}>",
                     text.as_ref()
-                        .map(|text| format!("'{text}'"))
+                        .map(|text| format!("'{}'", text.replace('\n', "\\n")))
                         .unwrap_or(format!("{length} characters")),
                     index
                 )?;
@@ -438,7 +478,10 @@ where
                 write!(
                     f,
                     "<insert '{}' from index {}>",
-                    text.iter().map(Token::original).collect::<String>(),
+                    text.iter()
+                        .map(Token::original)
+                        .collect::<String>()
+                        .replace('\n', "\\n"),
                     index
                 )
             }
@@ -455,7 +498,7 @@ where
                     "<delete {} from index {}>",
                     deleted_text
                         .as_ref()
-                        .map(|text| format!("'{text}'"))
+                        .map(|text| format!("'{}'", text.replace('\n', "\\n")))
                         .unwrap_or(format!("{deleted_character_count} characters")),
                     index
                 )?;
@@ -498,16 +541,26 @@ mod tests {
     #[test]
     fn test_apply_delete_with_create() {
         let builder = StringBuilder::new("hello world");
-        let operation = Operation::<()>::create_delete_with_text(5, " world".to_owned()).unwrap();
+        let delete_operation =
+            Operation::<()>::create_delete_with_text(0, "hello ".to_owned()).unwrap();
+        let retain_operation = Operation::<()>::create_equal(5, 5).unwrap();
 
-        assert_eq!(operation.apply(builder).build(), "hello");
+        let mut builder = delete_operation.apply(builder);
+        builder = retain_operation.apply(builder);
+
+        assert_eq!(builder.build(), "world");
     }
 
     #[test]
     fn test_apply_insert() {
         let builder = StringBuilder::new("hello");
-        let operation = Operation::create_insert(5, vec![" my friend".into()]).unwrap();
 
-        assert_eq!(operation.apply(builder).build(), "hello my friend");
+        let retain_operation = Operation::<()>::create_equal(5, 5).unwrap();
+        let insert_operation = Operation::create_insert(5, vec![" my friend".into()]).unwrap();
+
+        let mut builder = retain_operation.apply(builder);
+        builder = insert_operation.apply(builder);
+
+        assert_eq!(builder.build(), "hello my friend");
     }
 }
diff --git a/src/utils/string_builder.rs b/src/utils/string_builder.rs
index b19bcbb..8e37b79 100644
--- a/src/utils/string_builder.rs
+++ b/src/utils/string_builder.rs
@@ -1,78 +1,67 @@
 use core::ops::Range;
+use std::iter::Iterator;
 
-/// A helper for building a string in order based on an original string and a
-/// series of insertions and deletions applied to it. It is safe to use with
-/// UTF-8 strings as all operations are based on character indices.
-#[derive(Debug, Clone)]
+/// A helper for building a string in-order based on an original string and a
+/// series of insertions, deletions, and copies applied to it. It is safe to use
+/// with UTF-8 strings as all operations are based on character indices. The
+/// methods must be called in-order.
 pub struct StringBuilder<'a> {
-    original: &'a str,
-    last_old_char_index: usize,
+    original: Box<dyn Iterator<Item = char> + 'a>,
     buffer: String,
+
+    #[cfg(debug_assertions)]
+    remaining: String,
 }
 
 impl StringBuilder<'_> {
     pub fn new(original: &str) -> StringBuilder<'_> {
         StringBuilder {
-            original,
-            last_old_char_index: 0,
+            original: Box::new(original.chars()),
             buffer: String::with_capacity(original.len()),
+
+            #[cfg(debug_assertions)]
+            remaining: original.to_string(),
         }
     }
 
-    /// Insert a string at the given index after copying the original string up
-    /// to that index from the last insertion or deletion.
-    pub fn insert(&mut self, from: usize, text: &str) {
-        self.copy_until(from);
-        self.buffer.push_str(text);
+    /// Insert a string at the end of the built buffer.
+    pub fn insert(&mut self, text: &str) { self.buffer.push_str(text); }
+
+    /// Skip copying `length` characters from the original string to the built
+    /// buffer.
+    pub fn delete(&mut self, length: usize) {
+        if length == 0 {
+            return;
+        }
+
+        self.original.nth(length - 1);
+
+        if cfg!(debug_assertions) {
+            self.remaining = self.remaining.chars().skip(length).collect();
+        }
     }
 
-    /// Delete a string at the given index after copying the original string up
-    /// to that index from the last insertion or deletion.
-    pub fn delete(&mut self, range: core::ops::Range<usize>) {
-        self.copy_until(range.start);
-        self.last_old_char_index += range.len();
-    }
+    /// Copy `length` characters from the original string to the built buffer.
+    pub fn retain(&mut self, length: usize) {
+        self.buffer.extend(self.original.by_ref().take(length));
 
-    fn copy_until(&mut self, index: usize) {
-        let current_char_count = self.buffer.chars().count();
-        debug_assert!(
-            index >= current_char_count,
-            "String builder only support building in order"
-        );
-
-        let jump = index - current_char_count;
-
-        self.buffer.push_str(
-            &self
-                .original
-                .chars()
-                .skip(self.last_old_char_index)
-                .take(jump)
-                .collect::<String>(),
-        );
-        self.last_old_char_index += jump;
+        if cfg!(debug_assertions) {
+            self.remaining = self.remaining.chars().skip(length).collect();
+        }
     }
 
     /// Finish building the string after copying the remaining original string
     /// since the last insertion or deletion.
-    pub fn build(mut self) -> String {
-        self.buffer.push_str(
-            &self
-                .original
-                .chars()
-                .skip(self.last_old_char_index)
-                .collect::<String>(),
-        );
+    pub fn build(self) -> String { self.buffer }
 
-        self.buffer
-    }
-
-    #[allow(dead_code)]
+    #[cfg(debug_assertions)]
+    /// Get a slice of the built string and the remaining original string.
+    /// The implementation is quite suboptimal but it's only used for debugging.
     pub fn get_slice(&self, range: Range<usize>) -> String {
         let result = self
             .buffer
             .chars()
-            .chain(self.original.chars().skip(self.last_old_char_index))
+            .chain(self.remaining.chars())
             .skip(range.start)
             .take(range.end - range.start)
             .collect::<String>();
@@ -85,6 +74,8 @@ impl StringBuilder<'_> {
 
 #[cfg(test)]
 mod tests {
+    use pretty_assertions::assert_eq;
+
     use super::*;
 
     #[test]
@@ -92,20 +83,74 @@ mod tests {
         let original = "aaa bbb ccc";
         let mut builder = StringBuilder::new(original);
 
-        builder.insert(0, "ddd ");
-        builder.delete(4..8);
-        builder.insert(11, " eee");
+        builder.insert("ddd");
+        builder.delete(3);
+        builder.retain(8);
+        builder.insert(" eee");
 
         assert_eq!(builder.build(), "ddd bbb ccc eee");
-    }
 
-    #[test]
-    fn test_string_builder2() {
         let original = "abcde";
         let mut builder = StringBuilder::new(original);
 
-        builder.delete(1..4);
+        builder.retain(1);
+        builder.delete(3);
+        builder.retain(1);
 
         assert_eq!(builder.build(), "ae");
     }
+
+    #[test]
+    fn test_empty_original() {
+        let original = "";
+        let mut builder = StringBuilder::new(original);
+
+        builder.insert("test");
+        assert_eq!(builder.build(), "test");
+    }
+
+    #[test]
+    fn test_unicode_characters() {
+        let original = "こんにちは";
+        let mut builder = StringBuilder::new(original);
+
+        builder.retain(3);
+        builder.insert("世界, "); // Insert "World, "
+        builder.retain(2);
+
+        assert_eq!(builder.build(), "こんに世界, ちは");
+    }
+
+    #[test]
+    fn test_get_slice() {
+        let original = "abcdef";
+        let builder = StringBuilder::new(original);
+
+        // Test getting a slice of the original string
+        assert_eq!(builder.get_slice(1..4), "bcd");
+
+        // Test getting a slice that includes both buffer and remaining original
+        let mut builder = StringBuilder::new(original);
+        builder.retain(2); // "ab" in buffer
+        assert_eq!(builder.get_slice(1..5), "bcde");
+    }
+
+    #[test]
+    fn test_retain_all() {
+        let original = "Hello, world!";
+        let mut builder = StringBuilder::new(original);
+
+        builder.retain(original.len());
+        assert_eq!(builder.build(), original);
+    }
+
+    #[test]
+    fn test_delete_all() {
+        let original = "Hello";
+        let mut builder = StringBuilder::new(original);
+
+        builder.delete(original.len());
+        builder.insert("Hi");
+        assert_eq!(builder.build(), "Hi");
+    }
 }