diff --git a/frontend/rust-lib/flowy-grid/src/services/field/type_options/checkbox_type_option/checkbox_tests.rs b/frontend/rust-lib/flowy-grid/src/services/field/type_options/checkbox_type_option/checkbox_tests.rs
index b9d155da7d..ddd1ba049d 100644
--- a/frontend/rust-lib/flowy-grid/src/services/field/type_options/checkbox_type_option/checkbox_tests.rs
+++ b/frontend/rust-lib/flowy-grid/src/services/field/type_options/checkbox_type_option/checkbox_tests.rs
@@ -1,7 +1,7 @@
 #[cfg(test)]
 mod tests {
     use crate::entities::FieldType;
-    use crate::services::cell::{apply_cell_data_changeset, decode_any_cell_data, CellDataOperation};
+    use crate::services::cell::CellDataOperation;
     use crate::services::field::type_options::checkbox_type_option::*;
     use crate::services::field::FieldBuilder;
     use flowy_grid_data_model::revision::FieldRevision;
diff --git a/frontend/rust-lib/flowy-grid/src/services/field/type_options/date_type_option/date_tests.rs b/frontend/rust-lib/flowy-grid/src/services/field/type_options/date_type_option/date_tests.rs
index 74b6ee6fd8..1229a8f5e1 100644
--- a/frontend/rust-lib/flowy-grid/src/services/field/type_options/date_type_option/date_tests.rs
+++ b/frontend/rust-lib/flowy-grid/src/services/field/type_options/date_type_option/date_tests.rs
@@ -1,7 +1,7 @@
 #[cfg(test)]
 mod tests {
     use crate::entities::FieldType;
-    use crate::services::cell::{CellDataChangeset, CellDataOperation};
+    use crate::services::cell::CellDataOperation;
     use crate::services::field::*;
     // use crate::services::field::{DateCellChangeset, DateCellData, DateFormat, DateTypeOption, TimeFormat};
     use flowy_grid_data_model::revision::FieldRevision;
diff --git a/frontend/rust-lib/flowy-text-block/tests/editor/op_test.rs b/frontend/rust-lib/flowy-text-block/tests/editor/op_test.rs
index 3f174fa3bc..47d3c5ebfe 100644
--- a/frontend/rust-lib/flowy-text-block/tests/editor/op_test.rs
+++ b/frontend/rust-lib/flowy-text-block/tests/editor/op_test.rs
@@ -2,6 +2,7 @@
 use crate::editor::{Rng, TestBuilder, TestOp::*};
 use flowy_sync::client_document::{NewlineDoc, PlainDoc};
 use lib_ot::{
+    core::Interval,
     core::*,
     rich_text::{AttributeBuilder, RichTextAttribute, RichTextAttributes, RichTextDelta},
 };
@@ -39,23 +40,23 @@ fn attributes_insert_text_at_middle() {
 #[test]
 fn delta_get_ops_in_interval_1() {
     let mut delta = RichTextDelta::default();
-    let insert_a = OpBuilder::insert("123").build();
-    let insert_b = OpBuilder::insert("4").build();
+    let insert_a = OperationBuilder::insert("123").build();
+    let insert_b = OperationBuilder::insert("4").build();
 
     delta.add(insert_a.clone());
     delta.add(insert_b.clone());
 
-    let mut iterator = DeltaIter::from_interval(&delta, Interval::new(0, 4));
+    let mut iterator = DeltaIterator::from_interval(&delta, Interval::new(0, 4));
     assert_eq!(iterator.ops(), delta.ops);
 }
 
 #[test]
 fn delta_get_ops_in_interval_2() {
     let mut delta = RichTextDelta::default();
-    let insert_a = OpBuilder::insert("123").build();
-    let insert_b = OpBuilder::insert("4").build();
-    let insert_c = OpBuilder::insert("5").build();
-    let retain_a = OpBuilder::retain(3).build();
+    let insert_a = OperationBuilder::insert("123").build();
+    let insert_b = OperationBuilder::insert("4").build();
+    let insert_c = OperationBuilder::insert("5").build();
+    let retain_a = OperationBuilder::retain(3).build();
 
     delta.add(insert_a.clone());
     delta.add(retain_a.clone());
@@ -63,32 +64,32 @@ fn delta_get_ops_in_interval_2() {
     delta.add(insert_c.clone());
 
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(0, 2)).ops(),
-        vec![OpBuilder::insert("12").build()]
+        DeltaIterator::from_interval(&delta, Interval::new(0, 2)).ops(),
+        vec![OperationBuilder::insert("12").build()]
     );
 
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(1, 3)).ops(),
-        vec![OpBuilder::insert("23").build()]
+        DeltaIterator::from_interval(&delta, Interval::new(1, 3)).ops(),
+        vec![OperationBuilder::insert("23").build()]
     );
 
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(0, 3)).ops(),
+        DeltaIterator::from_interval(&delta, Interval::new(0, 3)).ops(),
         vec![insert_a.clone()]
     );
 
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(0, 4)).ops(),
-        vec![insert_a.clone(), OpBuilder::retain(1).build()]
+        DeltaIterator::from_interval(&delta, Interval::new(0, 4)).ops(),
+        vec![insert_a.clone(), OperationBuilder::retain(1).build()]
     );
 
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(0, 6)).ops(),
+        DeltaIterator::from_interval(&delta, Interval::new(0, 6)).ops(),
         vec![insert_a.clone(), retain_a.clone()]
     );
 
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(0, 7)).ops(),
+        DeltaIterator::from_interval(&delta, Interval::new(0, 7)).ops(),
         vec![insert_a.clone(), retain_a.clone(), insert_b.clone()]
     );
 }
@@ -96,54 +97,60 @@ fn delta_get_ops_in_interval_2() {
 #[test]
 fn delta_get_ops_in_interval_3() {
     let mut delta = RichTextDelta::default();
-    let insert_a = OpBuilder::insert("123456").build();
+    let insert_a = OperationBuilder::insert("123456").build();
     delta.add(insert_a.clone());
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(3, 5)).ops(),
-        vec![OpBuilder::insert("45").build()]
+        DeltaIterator::from_interval(&delta, Interval::new(3, 5)).ops(),
+        vec![OperationBuilder::insert("45").build()]
     );
 }
 
 #[test]
 fn delta_get_ops_in_interval_4() {
     let mut delta = RichTextDelta::default();
-    let insert_a = OpBuilder::insert("12").build();
-    let insert_b = OpBuilder::insert("34").build();
-    let insert_c = OpBuilder::insert("56").build();
+    let insert_a = OperationBuilder::insert("12").build();
+    let insert_b = OperationBuilder::insert("34").build();
+    let insert_c = OperationBuilder::insert("56").build();
 
     delta.ops.push(insert_a.clone());
     delta.ops.push(insert_b.clone());
     delta.ops.push(insert_c.clone());
 
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(0, 2)).ops(),
+        DeltaIterator::from_interval(&delta, Interval::new(0, 2)).ops(),
         vec![insert_a]
     );
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(2, 4)).ops(),
+        DeltaIterator::from_interval(&delta, Interval::new(2, 4)).ops(),
         vec![insert_b]
     );
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(4, 6)).ops(),
+        DeltaIterator::from_interval(&delta, Interval::new(4, 6)).ops(),
         vec![insert_c]
     );
 
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(2, 5)).ops(),
-        vec![OpBuilder::insert("34").build(), OpBuilder::insert("5").build()]
+        DeltaIterator::from_interval(&delta, Interval::new(2, 5)).ops(),
+        vec![
+            OperationBuilder::insert("34").build(),
+            OperationBuilder::insert("5").build()
+        ]
     );
 }
 
 #[test]
 fn delta_get_ops_in_interval_5() {
     let mut delta = RichTextDelta::default();
-    let insert_a = OpBuilder::insert("123456").build();
-    let insert_b = OpBuilder::insert("789").build();
+    let insert_a = OperationBuilder::insert("123456").build();
+    let insert_b = OperationBuilder::insert("789").build();
     delta.ops.push(insert_a.clone());
     delta.ops.push(insert_b.clone());
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(4, 8)).ops(),
-        vec![OpBuilder::insert("56").build(), OpBuilder::insert("78").build()]
+        DeltaIterator::from_interval(&delta, Interval::new(4, 8)).ops(),
+        vec![
+            OperationBuilder::insert("56").build(),
+            OperationBuilder::insert("78").build()
+        ]
     );
 
     // assert_eq!(
@@ -155,54 +162,60 @@ fn delta_get_ops_in_interval_5() {
 #[test]
 fn delta_get_ops_in_interval_6() {
     let mut delta = RichTextDelta::default();
-    let insert_a = OpBuilder::insert("12345678").build();
+    let insert_a = OperationBuilder::insert("12345678").build();
     delta.add(insert_a.clone());
     assert_eq!(
-        DeltaIter::from_interval(&delta, Interval::new(4, 6)).ops(),
-        vec![OpBuilder::insert("56").build()]
+        DeltaIterator::from_interval(&delta, Interval::new(4, 6)).ops(),
+        vec![OperationBuilder::insert("56").build()]
     );
 }
 
 #[test]
 fn delta_get_ops_in_interval_7() {
     let mut delta = RichTextDelta::default();
-    let insert_a = OpBuilder::insert("12345").build();
-    let retain_a = OpBuilder::retain(3).build();
+    let insert_a = OperationBuilder::insert("12345").build();
+    let retain_a = OperationBuilder::retain(3).build();
 
     delta.add(insert_a.clone());
     delta.add(retain_a.clone());
 
-    let mut iter_1 = DeltaIter::from_offset(&delta, 2);
-    assert_eq!(iter_1.next_op().unwrap(), OpBuilder::insert("345").build());
-    assert_eq!(iter_1.next_op().unwrap(), OpBuilder::retain(3).build());
+    let mut iter_1 = DeltaIterator::from_offset(&delta, 2);
+    assert_eq!(iter_1.next_op().unwrap(), OperationBuilder::insert("345").build());
+    assert_eq!(iter_1.next_op().unwrap(), OperationBuilder::retain(3).build());
 
-    let mut iter_2 = DeltaIter::new(&delta);
-    assert_eq!(iter_2.next_op_with_len(2).unwrap(), OpBuilder::insert("12").build());
-    assert_eq!(iter_2.next_op().unwrap(), OpBuilder::insert("345").build());
+    let mut iter_2 = DeltaIterator::new(&delta);
+    assert_eq!(
+        iter_2.next_op_with_len(2).unwrap(),
+        OperationBuilder::insert("12").build()
+    );
+    assert_eq!(iter_2.next_op().unwrap(), OperationBuilder::insert("345").build());
 
-    assert_eq!(iter_2.next_op().unwrap(), OpBuilder::retain(3).build());
+    assert_eq!(iter_2.next_op().unwrap(), OperationBuilder::retain(3).build());
 }
 
 #[test]
 fn delta_op_seek() {
     let mut delta = RichTextDelta::default();
-    let insert_a = OpBuilder::insert("12345").build();
-    let retain_a = OpBuilder::retain(3).build();
+    let insert_a = OperationBuilder::insert("12345").build();
+    let retain_a = OperationBuilder::retain(3).build();
     delta.add(insert_a.clone());
     delta.add(retain_a.clone());
-    let mut iter = DeltaIter::new(&delta);
+    let mut iter = DeltaIterator::new(&delta);
     iter.seek::<OpMetric>(1);
-    assert_eq!(iter.next_op().unwrap(), OpBuilder::retain(3).build());
+    assert_eq!(iter.next_op().unwrap(), retain_a);
 }
 
 #[test]
 fn delta_utf16_code_unit_seek() {
     let mut delta = RichTextDelta::default();
-    delta.add(OpBuilder::insert("12345").build());
+    delta.add(OperationBuilder::insert("12345").build());
 
-    let mut iter = DeltaIter::new(&delta);
+    let mut iter = DeltaIterator::new(&delta);
     iter.seek::<Utf16CodeUnitMetric>(3);
-    assert_eq!(iter.next_op_with_len(2).unwrap(), OpBuilder::insert("45").build());
+    assert_eq!(
+        iter.next_op_with_len(2).unwrap(),
+        OperationBuilder::insert("45").build()
+    );
 }
 
 #[test]
@@ -213,77 +226,92 @@ fn delta_utf16_code_unit_seek_with_attributes() {
         .add_attr(RichTextAttribute::Italic(true))
         .build();
 
-    delta.add(OpBuilder::insert("1234").attributes(attributes.clone()).build());
-    delta.add(OpBuilder::insert("\n").build());
+    delta.add(OperationBuilder::insert("1234").attributes(attributes.clone()).build());
+    delta.add(OperationBuilder::insert("\n").build());
 
-    let mut iter = DeltaIter::new(&delta);
+    let mut iter = DeltaIterator::new(&delta);
     iter.seek::<Utf16CodeUnitMetric>(0);
 
     assert_eq!(
         iter.next_op_with_len(4).unwrap(),
-        OpBuilder::insert("1234").attributes(attributes).build(),
+        OperationBuilder::insert("1234").attributes(attributes).build(),
     );
 }
 
 #[test]
 fn delta_next_op_len() {
     let mut delta = RichTextDelta::default();
-    delta.add(OpBuilder::insert("12345").build());
-    let mut iter = DeltaIter::new(&delta);
-    assert_eq!(iter.next_op_with_len(2).unwrap(), OpBuilder::insert("12").build());
-    assert_eq!(iter.next_op_with_len(2).unwrap(), OpBuilder::insert("34").build());
-    assert_eq!(iter.next_op_with_len(2).unwrap(), OpBuilder::insert("5").build());
+    delta.add(OperationBuilder::insert("12345").build());
+    let mut iter = DeltaIterator::new(&delta);
+    assert_eq!(
+        iter.next_op_with_len(2).unwrap(),
+        OperationBuilder::insert("12").build()
+    );
+    assert_eq!(
+        iter.next_op_with_len(2).unwrap(),
+        OperationBuilder::insert("34").build()
+    );
+    assert_eq!(iter.next_op_with_len(2).unwrap(), OperationBuilder::insert("5").build());
     assert_eq!(iter.next_op_with_len(1), None);
 }
 
 #[test]
 fn delta_next_op_len_with_chinese() {
     let mut delta = RichTextDelta::default();
-    delta.add(OpBuilder::insert("你好").build());
+    delta.add(OperationBuilder::insert("你好").build());
 
-    let mut iter = DeltaIter::new(&delta);
+    let mut iter = DeltaIterator::new(&delta);
     assert_eq!(iter.next_op_len().unwrap(), 2);
-    assert_eq!(iter.next_op_with_len(2).unwrap(), OpBuilder::insert("你好").build());
+    assert_eq!(
+        iter.next_op_with_len(2).unwrap(),
+        OperationBuilder::insert("你好").build()
+    );
 }
 
 #[test]
 fn delta_next_op_len_with_english() {
     let mut delta = RichTextDelta::default();
-    delta.add(OpBuilder::insert("ab").build());
-    let mut iter = DeltaIter::new(&delta);
+    delta.add(OperationBuilder::insert("ab").build());
+    let mut iter = DeltaIterator::new(&delta);
     assert_eq!(iter.next_op_len().unwrap(), 2);
-    assert_eq!(iter.next_op_with_len(2).unwrap(), OpBuilder::insert("ab").build());
+    assert_eq!(
+        iter.next_op_with_len(2).unwrap(),
+        OperationBuilder::insert("ab").build()
+    );
 }
 
 #[test]
 fn delta_next_op_len_after_seek() {
     let mut delta = RichTextDelta::default();
-    delta.add(OpBuilder::insert("12345").build());
-    let mut iter = DeltaIter::new(&delta);
+    delta.add(OperationBuilder::insert("12345").build());
+    let mut iter = DeltaIterator::new(&delta);
     assert_eq!(iter.next_op_len().unwrap(), 5);
     iter.seek::<Utf16CodeUnitMetric>(3);
     assert_eq!(iter.next_op_len().unwrap(), 2);
-    assert_eq!(iter.next_op_with_len(1).unwrap(), OpBuilder::insert("4").build());
+    assert_eq!(iter.next_op_with_len(1).unwrap(), OperationBuilder::insert("4").build());
     assert_eq!(iter.next_op_len().unwrap(), 1);
-    assert_eq!(iter.next_op().unwrap(), OpBuilder::insert("5").build());
+    assert_eq!(iter.next_op().unwrap(), OperationBuilder::insert("5").build());
 }
 
 #[test]
 fn delta_next_op_len_none() {
     let mut delta = RichTextDelta::default();
-    delta.add(OpBuilder::insert("12345").build());
-    let mut iter = DeltaIter::new(&delta);
+    delta.add(OperationBuilder::insert("12345").build());
+    let mut iter = DeltaIterator::new(&delta);
 
     assert_eq!(iter.next_op_len().unwrap(), 5);
-    assert_eq!(iter.next_op_with_len(5).unwrap(), OpBuilder::insert("12345").build());
+    assert_eq!(
+        iter.next_op_with_len(5).unwrap(),
+        OperationBuilder::insert("12345").build()
+    );
     assert_eq!(iter.next_op_len(), None);
 }
 
 #[test]
 fn delta_next_op_with_len_zero() {
     let mut delta = RichTextDelta::default();
-    delta.add(OpBuilder::insert("12345").build());
-    let mut iter = DeltaIter::new(&delta);
+    delta.add(OperationBuilder::insert("12345").build());
+    let mut iter = DeltaIterator::new(&delta);
     assert_eq!(iter.next_op_with_len(0), None,);
     assert_eq!(iter.next_op_len().unwrap(), 5);
 }
@@ -291,14 +319,14 @@ fn delta_next_op_with_len_zero() {
 #[test]
 fn delta_next_op_with_len_cross_op_return_last() {
     let mut delta = RichTextDelta::default();
-    delta.add(OpBuilder::insert("12345").build());
-    delta.add(OpBuilder::retain(1).build());
-    delta.add(OpBuilder::insert("678").build());
+    delta.add(OperationBuilder::insert("12345").build());
+    delta.add(OperationBuilder::retain(1).build());
+    delta.add(OperationBuilder::insert("678").build());
 
-    let mut iter = DeltaIter::new(&delta);
+    let mut iter = DeltaIterator::new(&delta);
     iter.seek::<Utf16CodeUnitMetric>(4);
     assert_eq!(iter.next_op_len().unwrap(), 1);
-    assert_eq!(iter.next_op_with_len(2).unwrap(), OpBuilder::retain(1).build());
+    assert_eq!(iter.next_op_with_len(2).unwrap(), OperationBuilder::retain(1).build());
 }
 
 #[test]
@@ -342,18 +370,17 @@ fn apply_1000() {
 }
 
 #[test]
-fn apply() {
-    let s = "hello world,".to_owned();
-    let mut delta_a = RichTextDelta::default();
-    delta_a.insert(&s, RichTextAttributes::default());
+fn apply_test() {
+    let s = "hello";
+    let delta_a = PlainTextDeltaBuilder::new().insert(s).build();
+    let delta_b = PlainTextDeltaBuilder::new()
+        .retain(s.len())
+        .insert(", AppFlowy")
+        .build();
 
-    let mut delta_b = RichTextDelta::default();
-    delta_b.retain(s.len(), RichTextAttributes::default());
-    delta_b.insert("appflowy", RichTextAttributes::default());
-
-    let after_a = delta_a.apply("").unwrap();
+    let after_a = delta_a.to_str().unwrap();
     let after_b = delta_b.apply(&after_a).unwrap();
-    assert_eq!("hello world,appflowy", &after_b);
+    assert_eq!("hello, AppFlowy", &after_b);
 }
 
 #[test]
@@ -384,6 +411,17 @@ fn invert() {
     }
 }
 
+#[test]
+fn invert_test() {
+    let s = "hello world";
+    let delta = PlainTextDeltaBuilder::new().insert(s).build();
+    let invert_delta = delta.invert_str("");
+    assert_eq!(delta.utf16_base_len, invert_delta.utf16_target_len);
+    assert_eq!(delta.utf16_target_len, invert_delta.utf16_base_len);
+
+    assert_eq!(invert_delta.apply(s).unwrap(), "")
+}
+
 #[test]
 fn empty_ops() {
     let mut delta = RichTextDelta::default();
@@ -415,23 +453,24 @@ fn ops_merging() {
     assert_eq!(delta.ops.len(), 0);
     delta.retain(2, RichTextAttributes::default());
     assert_eq!(delta.ops.len(), 1);
-    assert_eq!(delta.ops.last(), Some(&OpBuilder::retain(2).build()));
+    assert_eq!(delta.ops.last(), Some(&OperationBuilder::retain(2).build()));
     delta.retain(3, RichTextAttributes::default());
     assert_eq!(delta.ops.len(), 1);
-    assert_eq!(delta.ops.last(), Some(&OpBuilder::retain(5).build()));
+    assert_eq!(delta.ops.last(), Some(&OperationBuilder::retain(5).build()));
     delta.insert("abc", RichTextAttributes::default());
     assert_eq!(delta.ops.len(), 2);
-    assert_eq!(delta.ops.last(), Some(&OpBuilder::insert("abc").build()));
+    assert_eq!(delta.ops.last(), Some(&OperationBuilder::insert("abc").build()));
     delta.insert("xyz", RichTextAttributes::default());
     assert_eq!(delta.ops.len(), 2);
-    assert_eq!(delta.ops.last(), Some(&OpBuilder::insert("abcxyz").build()));
+    assert_eq!(delta.ops.last(), Some(&OperationBuilder::insert("abcxyz").build()));
     delta.delete(1);
     assert_eq!(delta.ops.len(), 3);
-    assert_eq!(delta.ops.last(), Some(&OpBuilder::delete(1).build()));
+    assert_eq!(delta.ops.last(), Some(&OperationBuilder::delete(1).build()));
     delta.delete(1);
     assert_eq!(delta.ops.len(), 3);
-    assert_eq!(delta.ops.last(), Some(&OpBuilder::delete(2).build()));
+    assert_eq!(delta.ops.last(), Some(&OperationBuilder::delete(2).build()));
 }
+
 #[test]
 fn is_noop() {
     let mut delta = RichTextDelta::default();
@@ -582,11 +621,11 @@ fn transform_two_conflict_non_seq_delta() {
 #[test]
 fn delta_invert_no_attribute_delta() {
     let mut delta = RichTextDelta::default();
-    delta.add(OpBuilder::insert("123").build());
+    delta.add(OperationBuilder::insert("123").build());
 
     let mut change = RichTextDelta::default();
-    change.add(OpBuilder::retain(3).build());
-    change.add(OpBuilder::insert("456").build());
+    change.add(OperationBuilder::retain(3).build());
+    change.add(OperationBuilder::insert("456").build());
     let undo = change.invert(&delta);
 
     let new_delta = delta.compose(&change).unwrap();
diff --git a/frontend/rust-lib/flowy-text-block/tests/editor/serde_test.rs b/frontend/rust-lib/flowy-text-block/tests/editor/serde_test.rs
index 87d425901b..ae9e57b3c6 100644
--- a/frontend/rust-lib/flowy-text-block/tests/editor/serde_test.rs
+++ b/frontend/rust-lib/flowy-text-block/tests/editor/serde_test.rs
@@ -11,7 +11,7 @@ fn operation_insert_serialize_test() {
         .add_attr(RichTextAttribute::Bold(true))
         .add_attr(RichTextAttribute::Italic(true))
         .build();
-    let operation = OpBuilder::insert("123").attributes(attributes).build();
+    let operation = OperationBuilder::insert("123").attributes(attributes).build();
     let json = serde_json::to_string(&operation).unwrap();
     eprintln!("{}", json);
 
@@ -42,7 +42,7 @@ fn attributes_serialize_test() {
         .add_attr(RichTextAttribute::Bold(true))
         .add_attr(RichTextAttribute::Italic(true))
         .build();
-    let retain = OpBuilder::insert("123").attributes(attributes).build();
+    let retain = OperationBuilder::insert("123").attributes(attributes).build();
 
     let json = serde_json::to_string(&retain).unwrap();
     eprintln!("{}", json);
@@ -56,7 +56,7 @@ fn delta_serialize_multi_attribute_test() {
         .add_attr(RichTextAttribute::Bold(true))
         .add_attr(RichTextAttribute::Italic(true))
         .build();
-    let retain = OpBuilder::insert("123").attributes(attributes).build();
+    let retain = OperationBuilder::insert("123").attributes(attributes).build();
 
     delta.add(retain);
     delta.add(Operation::Retain(5.into()));
diff --git a/frontend/rust-lib/flowy-text-block/tests/editor/undo_redo_test.rs b/frontend/rust-lib/flowy-text-block/tests/editor/undo_redo_test.rs
index e6ea9200ab..78aa034744 100644
--- a/frontend/rust-lib/flowy-text-block/tests/editor/undo_redo_test.rs
+++ b/frontend/rust-lib/flowy-text-block/tests/editor/undo_redo_test.rs
@@ -108,6 +108,7 @@ fn history_bold_redo_with_lagging() {
 fn history_delete_undo() {
     let ops = vec![
         Insert(0, "123", 0),
+        Wait(RECORD_THRESHOLD),
         AssertDocJson(0, r#"[{"insert":"123"}]"#),
         Delete(0, Interval::new(0, 3)),
         AssertDocJson(0, r#"[]"#),
diff --git a/shared-lib/flowy-sync/src/client_document/extensions/delete/preserve_line_format_merge.rs b/shared-lib/flowy-sync/src/client_document/extensions/delete/preserve_line_format_merge.rs
index 4da15e5f06..6c7283e4c7 100644
--- a/shared-lib/flowy-sync/src/client_document/extensions/delete/preserve_line_format_merge.rs
+++ b/shared-lib/flowy-sync/src/client_document/extensions/delete/preserve_line_format_merge.rs
@@ -1,6 +1,6 @@
 use crate::{client_document::DeleteExt, util::is_newline};
 use lib_ot::{
-    core::{Attributes, DeltaBuilder, DeltaIter, Interval, Utf16CodeUnitMetric, NEW_LINE},
+    core::{Attributes, DeltaBuilder, DeltaIterator, Interval, Utf16CodeUnitMetric, NEW_LINE},
     rich_text::{plain_attributes, RichTextDelta},
 };
 
@@ -16,7 +16,7 @@ impl DeleteExt for PreserveLineFormatOnMerge {
         }
 
         // seek to the  interval start pos. e.g. You backspace enter pos
-        let mut iter = DeltaIter::from_offset(delta, interval.start);
+        let mut iter = DeltaIterator::from_offset(delta, interval.start);
 
         // op will be the "\n"
         let newline_op = iter.next_op_with_len(1)?;
diff --git a/shared-lib/flowy-sync/src/client_document/extensions/format/resolve_block_format.rs b/shared-lib/flowy-sync/src/client_document/extensions/format/resolve_block_format.rs
index 46a0e0290d..4a4c00a19d 100644
--- a/shared-lib/flowy-sync/src/client_document/extensions/format/resolve_block_format.rs
+++ b/shared-lib/flowy-sync/src/client_document/extensions/format/resolve_block_format.rs
@@ -1,5 +1,5 @@
 use lib_ot::{
-    core::{DeltaBuilder, DeltaIter, Interval},
+    core::{DeltaBuilder, DeltaIterator, Interval},
     rich_text::{plain_attributes, AttributeScope, RichTextAttribute, RichTextDelta},
 };
 
@@ -20,7 +20,7 @@ impl FormatExt for ResolveBlockFormat {
         }
 
         let mut new_delta = DeltaBuilder::new().retain(interval.start).build();
-        let mut iter = DeltaIter::from_offset(delta, interval.start);
+        let mut iter = DeltaIterator::from_offset(delta, interval.start);
         let mut start = 0;
         let end = interval.size();
         while start < end && iter.has_next() {
diff --git a/shared-lib/flowy-sync/src/client_document/extensions/format/resolve_inline_format.rs b/shared-lib/flowy-sync/src/client_document/extensions/format/resolve_inline_format.rs
index 383b780aca..567d06d6f2 100644
--- a/shared-lib/flowy-sync/src/client_document/extensions/format/resolve_inline_format.rs
+++ b/shared-lib/flowy-sync/src/client_document/extensions/format/resolve_inline_format.rs
@@ -1,5 +1,5 @@
 use lib_ot::{
-    core::{DeltaBuilder, DeltaIter, Interval},
+    core::{DeltaBuilder, DeltaIterator, Interval},
     rich_text::{AttributeScope, RichTextAttribute, RichTextDelta},
 };
 
@@ -19,7 +19,7 @@ impl FormatExt for ResolveInlineFormat {
             return None;
         }
         let mut new_delta = DeltaBuilder::new().retain(interval.start).build();
-        let mut iter = DeltaIter::from_offset(delta, interval.start);
+        let mut iter = DeltaIterator::from_offset(delta, interval.start);
         let mut start = 0;
         let end = interval.size();
 
diff --git a/shared-lib/flowy-sync/src/client_document/extensions/insert/auto_exit_block.rs b/shared-lib/flowy-sync/src/client_document/extensions/insert/auto_exit_block.rs
index e41470b9eb..253833d255 100644
--- a/shared-lib/flowy-sync/src/client_document/extensions/insert/auto_exit_block.rs
+++ b/shared-lib/flowy-sync/src/client_document/extensions/insert/auto_exit_block.rs
@@ -1,8 +1,6 @@
 use crate::{client_document::InsertExt, util::is_newline};
-use lib_ot::{
-    core::{is_empty_line_at_index, DeltaBuilder, DeltaIter},
-    rich_text::{attributes_except_header, RichTextAttributeKey, RichTextDelta},
-};
+use lib_ot::core::{is_empty_line_at_index, DeltaBuilder, DeltaIterator};
+use lib_ot::rich_text::{attributes_except_header, RichTextAttributeKey, RichTextDelta};
 
 pub struct AutoExitBlock {}
 
@@ -21,7 +19,7 @@ impl InsertExt for AutoExitBlock {
             return None;
         }
 
-        let mut iter = DeltaIter::from_offset(delta, index);
+        let mut iter = DeltaIterator::from_offset(delta, index);
         let next = iter.next_op()?;
         let mut attributes = next.get_attributes();
 
diff --git a/shared-lib/flowy-sync/src/client_document/extensions/insert/auto_format.rs b/shared-lib/flowy-sync/src/client_document/extensions/insert/auto_format.rs
index d7f1da4f89..4c7cd642c2 100644
--- a/shared-lib/flowy-sync/src/client_document/extensions/insert/auto_format.rs
+++ b/shared-lib/flowy-sync/src/client_document/extensions/insert/auto_format.rs
@@ -1,6 +1,6 @@
 use crate::{client_document::InsertExt, util::is_whitespace};
 use lib_ot::{
-    core::{count_utf16_code_units, DeltaBuilder, DeltaIter},
+    core::{count_utf16_code_units, DeltaBuilder, DeltaIterator},
     rich_text::{plain_attributes, RichTextAttribute, RichTextAttributes, RichTextDelta},
 };
 use std::cmp::min;
@@ -17,7 +17,7 @@ impl InsertExt for AutoFormatExt {
         if !is_whitespace(text) {
             return None;
         }
-        let mut iter = DeltaIter::new(delta);
+        let mut iter = DeltaIterator::new(delta);
         if let Some(prev) = iter.next_op_with_len(index) {
             match AutoFormat::parse(prev.get_data()) {
                 None => {}
diff --git a/shared-lib/flowy-sync/src/client_document/extensions/insert/default_insert.rs b/shared-lib/flowy-sync/src/client_document/extensions/insert/default_insert.rs
index 628d55cb24..c165985493 100644
--- a/shared-lib/flowy-sync/src/client_document/extensions/insert/default_insert.rs
+++ b/shared-lib/flowy-sync/src/client_document/extensions/insert/default_insert.rs
@@ -1,6 +1,6 @@
 use crate::client_document::InsertExt;
 use lib_ot::{
-    core::{Attributes, DeltaBuilder, DeltaIter, NEW_LINE},
+    core::{Attributes, DeltaBuilder, DeltaIterator, NEW_LINE},
     rich_text::{RichTextAttributeKey, RichTextAttributes, RichTextDelta},
 };
 
@@ -11,7 +11,7 @@ impl InsertExt for DefaultInsertAttribute {
     }
 
     fn apply(&self, delta: &RichTextDelta, replace_len: usize, text: &str, index: usize) -> Option<RichTextDelta> {
-        let iter = DeltaIter::new(delta);
+        let iter = DeltaIterator::new(delta);
         let mut attributes = RichTextAttributes::new();
 
         // Enable each line split by "\n" remains the block attributes. for example:
diff --git a/shared-lib/flowy-sync/src/client_document/extensions/insert/preserve_block_format.rs b/shared-lib/flowy-sync/src/client_document/extensions/insert/preserve_block_format.rs
index 2c0ceae111..03c9723d7b 100644
--- a/shared-lib/flowy-sync/src/client_document/extensions/insert/preserve_block_format.rs
+++ b/shared-lib/flowy-sync/src/client_document/extensions/insert/preserve_block_format.rs
@@ -1,6 +1,6 @@
 use crate::{client_document::InsertExt, util::is_newline};
 use lib_ot::{
-    core::{DeltaBuilder, DeltaIter, NEW_LINE},
+    core::{DeltaBuilder, DeltaIterator, NEW_LINE},
     rich_text::{
         attributes_except_header, plain_attributes, RichTextAttribute, RichTextAttributeKey, RichTextAttributes,
         RichTextDelta,
@@ -18,7 +18,7 @@ impl InsertExt for PreserveBlockFormatOnInsert {
             return None;
         }
 
-        let mut iter = DeltaIter::from_offset(delta, index);
+        let mut iter = DeltaIterator::from_offset(delta, index);
         match iter.next_op_with_newline() {
             None => {}
             Some((newline_op, offset)) => {
diff --git a/shared-lib/flowy-sync/src/client_document/extensions/insert/preserve_inline_format.rs b/shared-lib/flowy-sync/src/client_document/extensions/insert/preserve_inline_format.rs
index 37b31e3d26..b0de6451aa 100644
--- a/shared-lib/flowy-sync/src/client_document/extensions/insert/preserve_inline_format.rs
+++ b/shared-lib/flowy-sync/src/client_document/extensions/insert/preserve_inline_format.rs
@@ -3,7 +3,7 @@ use crate::{
     util::{contain_newline, is_newline},
 };
 use lib_ot::{
-    core::{DeltaBuilder, DeltaIter, OpNewline, NEW_LINE},
+    core::{DeltaBuilder, DeltaIterator, OpNewline, NEW_LINE},
     rich_text::{plain_attributes, RichTextAttributeKey, RichTextDelta},
 };
 
@@ -18,7 +18,7 @@ impl InsertExt for PreserveInlineFormat {
             return None;
         }
 
-        let mut iter = DeltaIter::new(delta);
+        let mut iter = DeltaIterator::new(delta);
         let prev = iter.next_op_with_len(index)?;
         if OpNewline::parse(&prev).is_contain() {
             return None;
@@ -64,7 +64,7 @@ impl InsertExt for PreserveLineFormatOnSplit {
             return None;
         }
 
-        let mut iter = DeltaIter::new(delta);
+        let mut iter = DeltaIterator::new(delta);
         let prev = iter.next_op_with_len(index)?;
         if OpNewline::parse(&prev).is_end() {
             return None;
diff --git a/shared-lib/flowy-sync/src/client_document/extensions/insert/reset_format_on_new_line.rs b/shared-lib/flowy-sync/src/client_document/extensions/insert/reset_format_on_new_line.rs
index f63bf9bddf..8671049ee7 100644
--- a/shared-lib/flowy-sync/src/client_document/extensions/insert/reset_format_on_new_line.rs
+++ b/shared-lib/flowy-sync/src/client_document/extensions/insert/reset_format_on_new_line.rs
@@ -1,6 +1,6 @@
 use crate::{client_document::InsertExt, util::is_newline};
 use lib_ot::{
-    core::{DeltaBuilder, DeltaIter, Utf16CodeUnitMetric, NEW_LINE},
+    core::{DeltaBuilder, DeltaIterator, Utf16CodeUnitMetric, NEW_LINE},
     rich_text::{RichTextAttributeKey, RichTextAttributes, RichTextDelta},
 };
 
@@ -15,7 +15,7 @@ impl InsertExt for ResetLineFormatOnNewLine {
             return None;
         }
 
-        let mut iter = DeltaIter::new(delta);
+        let mut iter = DeltaIterator::new(delta);
         iter.seek::<Utf16CodeUnitMetric>(index);
         let next_op = iter.next_op()?;
         if !next_op.get_data().starts_with(NEW_LINE) {
diff --git a/shared-lib/lib-ot/src/core/delta/builder.rs b/shared-lib/lib-ot/src/core/delta/builder.rs
index b065b645af..184284393a 100644
--- a/shared-lib/lib-ot/src/core/delta/builder.rs
+++ b/shared-lib/lib-ot/src/core/delta/builder.rs
@@ -1,7 +1,12 @@
-use crate::core::{trim, Attributes, Delta, PlainTextAttributes};
+use crate::core::delta::{trim, Delta};
+use crate::core::operation::{Attributes, PlainTextAttributes};
 
 pub type PlainTextDeltaBuilder = DeltaBuilder<PlainTextAttributes>;
 
+/// A builder for creating new [Delta] objects.
+///
+/// Note that all edit operations must be sorted; the start point of each
+/// interval must be no less than the end point of the previous one.
 pub struct DeltaBuilder<T: Attributes> {
     delta: Delta<T>,
 }
@@ -23,6 +28,8 @@ where
         DeltaBuilder::default()
     }
 
+    /// Retain the 'n' characters with the attributes. Use 'retain' instead if you don't
+    /// need any attributes.
     pub fn retain_with_attributes(mut self, n: usize, attrs: T) -> Self {
         self.delta.retain(n, attrs);
         self
@@ -33,11 +40,14 @@ where
         self
     }
 
+    /// Deletes the given interval. Panics if interval is not properly sorted.
     pub fn delete(mut self, n: usize) -> Self {
         self.delta.delete(n);
         self
     }
 
+    /// Insert the string with attributes. Use 'insert' instead if you don't
+    /// need any attributes.
     pub fn insert_with_attributes(mut self, s: &str, attrs: T) -> Self {
         self.delta.insert(s, attrs);
         self
@@ -53,6 +63,7 @@ where
         self
     }
 
+    /// Builds the `Delta`
     pub fn build(self) -> Delta<T> {
         self.delta
     }
diff --git a/shared-lib/lib-ot/src/core/delta/cursor.rs b/shared-lib/lib-ot/src/core/delta/cursor.rs
index d6ebb8b3cc..a465d62dea 100644
--- a/shared-lib/lib-ot/src/core/delta/cursor.rs
+++ b/shared-lib/lib-ot/src/core/delta/cursor.rs
@@ -1,33 +1,51 @@
 #![allow(clippy::while_let_on_iterator)]
-use crate::{
-    core::{Attributes, Delta, Interval, Operation},
-    errors::{ErrorBuilder, OTError, OTErrorCode},
-};
+use crate::core::delta::Delta;
+use crate::core::interval::Interval;
+use crate::core::operation::{Attributes, Operation};
+use crate::errors::{ErrorBuilder, OTError, OTErrorCode};
 use std::{cmp::min, iter::Enumerate, slice::Iter};
 
+/// A [DeltaCursor] is used to iterate the delta and return the corresponding delta.
 #[derive(Debug)]
-pub struct OpCursor<'a, T: Attributes> {
+pub struct DeltaCursor<'a, T: Attributes> {
     pub(crate) delta: &'a Delta<T>,
     pub(crate) origin_iv: Interval,
     pub(crate) consume_iv: Interval,
     pub(crate) consume_count: usize,
-    pub(crate) op_index: usize,
+    pub(crate) op_offset: usize,
     iter: Enumerate<Iter<'a, Operation<T>>>,
     next_op: Option<Operation<T>>,
 }
 
-impl<'a, T> OpCursor<'a, T>
+impl<'a, T> DeltaCursor<'a, T>
 where
     T: Attributes,
 {
-    pub fn new(delta: &'a Delta<T>, interval: Interval) -> OpCursor<'a, T> {
+    /// # Arguments
+    ///
+    /// * `delta`: The delta you want to iterate over.
+    /// * `interval`: The range for the cursor movement.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use lib_ot::core::{DeltaIterator, Interval, OperationBuilder};
+    /// use lib_ot::rich_text::RichTextDelta;
+    /// let mut delta = RichTextDelta::default();   
+    /// let op_1 = OperationBuilder::insert("123").build();    
+    /// let op_2 = OperationBuilder::insert("4").build();
+    /// delta.add(op_1.clone());
+    /// delta.add(op_2.clone());
+    /// assert_eq!(DeltaIterator::from_interval(&delta, Interval::new(0, 3)).ops(), vec![op_1.clone()]);
+    /// ```
+    pub fn new(delta: &'a Delta<T>, interval: Interval) -> DeltaCursor<'a, T> {
         // debug_assert!(interval.start <= delta.target_len);
         let mut cursor = Self {
             delta,
             origin_iv: interval,
             consume_iv: interval,
             consume_count: 0,
-            op_index: 0,
+            op_offset: 0,
             iter: delta.ops.iter().enumerate(),
             next_op: None,
         };
@@ -35,17 +53,37 @@ where
         cursor
     }
 
-    // get the next operation interval
+    /// Return the next operation interval
     pub fn next_iv(&self) -> Interval {
         self.next_iv_with_len(None).unwrap_or_else(|| Interval::new(0, 0))
     }
 
-    pub fn next_op(&mut self) -> Option<Operation<T>> {
+    /// Return the next operation
+    pub fn get_next_op(&mut self) -> Option<Operation<T>> {
         self.next_with_len(None)
     }
 
-    // get the last operation before the end.
-    // checkout the delta_next_op_with_len_cross_op_return_last test for more detail
+    /// Return the reference of the next operation
+    pub fn next_op(&self) -> Option<&Operation<T>> {
+        let mut next_op = self.next_op.as_ref();
+        if next_op.is_none() {
+            let mut offset = 0;
+            for op in &self.delta.ops {
+                offset += op.len();
+                if offset > self.consume_count {
+                    next_op = Some(op);
+                    break;
+                }
+            }
+        }
+        next_op
+    }
+
+    /// # Arguments
+    ///
+    /// * `expected_len`: Return the next operation with the specified length.
+    ///
+    ///
     pub fn next_with_len(&mut self, expected_len: Option<usize>) -> Option<Operation<T>> {
         let mut find_op = None;
         let holder = self.next_op.clone();
@@ -97,17 +135,24 @@ where
     }
 
     pub fn has_next(&self) -> bool {
-        self.next_iter_op().is_some()
+        self.next_op().is_some()
     }
 
-    fn descend(&mut self, index: usize) {
-        self.consume_iv.start += index;
+    /// Find the op within the current offset.
+    /// This function sets the start of the consume_iv to the offset, update the consume_count
+    /// and the next_op reference.
+    ///
+    /// # Arguments
+    ///
+    /// * `offset`: Represents the offset of the delta string, in Utf16CodeUnit unit.
+    fn descend(&mut self, offset: usize) {
+        self.consume_iv.start += offset;
 
         if self.consume_count >= self.consume_iv.start {
             return;
         }
         while let Some((o_index, op)) = self.iter.next() {
-            self.op_index = o_index;
+            self.op_offset = o_index;
             let start = self.consume_count;
             let end = start + op.len();
             let intersect = Interval::new(start, end).intersect(self.consume_iv);
@@ -121,7 +166,7 @@ where
     }
 
     fn next_iv_with_len(&self, expected_len: Option<usize>) -> Option<Interval> {
-        let op = self.next_iter_op()?;
+        let op = self.next_op()?;
         let start = self.consume_count;
         let end = match expected_len {
             None => self.consume_count + op.len(),
@@ -132,31 +177,16 @@ where
         let interval = intersect.translate_neg(start);
         Some(interval)
     }
-
-    pub fn next_iter_op(&self) -> Option<&Operation<T>> {
-        let mut next_op = self.next_op.as_ref();
-        if next_op.is_none() {
-            let mut offset = 0;
-            for op in &self.delta.ops {
-                offset += op.len();
-                if offset > self.consume_count {
-                    next_op = Some(op);
-                    break;
-                }
-            }
-        }
-        next_op
-    }
 }
 
-fn find_next<'a, T>(cursor: &mut OpCursor<'a, T>) -> Option<&'a Operation<T>>
+fn find_next<'a, T>(cursor: &mut DeltaCursor<'a, T>) -> Option<&'a Operation<T>>
 where
     T: Attributes,
 {
     match cursor.iter.next() {
         None => None,
         Some((o_index, op)) => {
-            cursor.op_index = o_index;
+            cursor.op_offset = o_index;
             Some(op)
         }
     }
@@ -164,31 +194,34 @@ where
 
 type SeekResult = Result<(), OTError>;
 pub trait Metric {
-    fn seek<T: Attributes>(cursor: &mut OpCursor<T>, offset: usize) -> SeekResult;
+    fn seek<T: Attributes>(cursor: &mut DeltaCursor<T>, offset: usize) -> SeekResult;
 }
 
+/// [OpMetric] is used by [DeltaIterator] for seeking operations
+/// The unit of the movement is Operation
 pub struct OpMetric();
 
 impl Metric for OpMetric {
-    fn seek<T: Attributes>(cursor: &mut OpCursor<T>, offset: usize) -> SeekResult {
-        let _ = check_bound(cursor.op_index, offset)?;
-        let mut seek_cursor = OpCursor::new(cursor.delta, cursor.origin_iv);
-        let mut cur_offset = 0;
+    fn seek<T: Attributes>(cursor: &mut DeltaCursor<T>, op_offset: usize) -> SeekResult {
+        let _ = check_bound(cursor.op_offset, op_offset)?;
+        let mut seek_cursor = DeltaCursor::new(cursor.delta, cursor.origin_iv);
+
         while let Some((_, op)) = seek_cursor.iter.next() {
-            cur_offset += op.len();
-            if cur_offset > offset {
+            cursor.descend(op.len());
+            if cursor.op_offset >= op_offset {
                 break;
             }
         }
-        cursor.descend(cur_offset);
         Ok(())
     }
 }
 
+/// [Utf16CodeUnitMetric] is used by [DeltaIterator] for seeking operations.
+/// The unit of the movement is Utf16CodeUnit
 pub struct Utf16CodeUnitMetric();
 
 impl Metric for Utf16CodeUnitMetric {
-    fn seek<T: Attributes>(cursor: &mut OpCursor<T>, offset: usize) -> SeekResult {
+    fn seek<T: Attributes>(cursor: &mut DeltaCursor<T>, offset: usize) -> SeekResult {
         if offset > 0 {
             let _ = check_bound(cursor.consume_count, offset)?;
             let _ = cursor.next_with_len(Some(offset));
diff --git a/shared-lib/lib-ot/src/core/delta/delta.rs b/shared-lib/lib-ot/src/core/delta/delta.rs
index 29fd424dcb..6edf817bdf 100644
--- a/shared-lib/lib-ot/src/core/delta/delta.rs
+++ b/shared-lib/lib-ot/src/core/delta/delta.rs
@@ -1,8 +1,9 @@
-use crate::{
-    core::{operation::*, DeltaIter, FlowyStr, Interval, OperationTransformable, MAX_IV_LEN},
-    errors::{ErrorBuilder, OTError, OTErrorCode},
-};
+use crate::errors::{ErrorBuilder, OTError, OTErrorCode};
 
+use crate::core::delta::{DeltaIterator, MAX_IV_LEN};
+use crate::core::flowy_str::FlowyStr;
+use crate::core::interval::Interval;
+use crate::core::operation::{Attributes, Operation, OperationBuilder, OperationTransformable, PlainTextAttributes};
 use bytes::Bytes;
 use serde::de::DeserializeOwned;
 use std::{
@@ -15,11 +16,20 @@ use std::{
 
 pub type PlainTextDelta = Delta<PlainTextAttributes>;
 
-// TODO: optimize the memory usage with Arc::make_mut or Cow
+/// A [Delta] contains list of operations that consists of 'Retain', 'Delete' and 'Insert' operation.
+/// Check out the [Operation] for more details. It describes the document as a sequence of
+/// operations.
+///
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct Delta<T: Attributes> {
     pub ops: Vec<Operation<T>>,
+
+    /// 'Delete' and 'Retain' operation will update the [utf16_base_len]
+    /// Transforming the other delta, it requires the utf16_base_len must be equal.  
     pub utf16_base_len: usize,
+
+    /// Represents the current len of the delta.
+    /// 'Insert' and 'Retain' operation will update the [utf16_target_len]
     pub utf16_target_len: usize,
 }
 
@@ -81,6 +91,7 @@ where
         }
     }
 
+    /// Adding an operation. It will be added in sequence.
     pub fn add(&mut self, op: Operation<T>) {
         match op {
             Operation::Delete(i) => self.delete(i),
@@ -89,6 +100,7 @@ where
         }
     }
 
+    /// Creating a [Delete] operation with len [n]
     pub fn delete(&mut self, n: usize) {
         if n == 0 {
             return;
@@ -97,10 +109,11 @@ where
         if let Some(Operation::Delete(n_last)) = self.ops.last_mut() {
             *n_last += n;
         } else {
-            self.ops.push(OpBuilder::delete(n).build());
+            self.ops.push(OperationBuilder::delete(n).build());
         }
     }
 
+    /// Creating a [Insert] operation with string, [s].
     pub fn insert(&mut self, s: &str, attributes: T) {
         let s: FlowyStr = s.into();
         if s.is_empty() {
@@ -119,10 +132,10 @@ where
             }
             [.., op_last @ Operation::<T>::Delete(_)] => {
                 let new_last = op_last.clone();
-                *op_last = OpBuilder::<T>::insert(&s).attributes(attributes).build();
+                *op_last = OperationBuilder::<T>::insert(&s).attributes(attributes).build();
                 Some(new_last)
             }
-            _ => Some(OpBuilder::<T>::insert(&s).attributes(attributes).build()),
+            _ => Some(OperationBuilder::<T>::insert(&s).attributes(attributes).build()),
         };
 
         match new_last {
@@ -131,6 +144,7 @@ where
         }
     }
 
+    /// Creating a [Retain] operation with len, [n].
     pub fn retain(&mut self, n: usize, attributes: T) {
         if n == 0 {
             return;
@@ -143,24 +157,48 @@ where
                 self.ops.push(new_op);
             }
         } else {
-            self.ops.push(OpBuilder::<T>::retain(n).attributes(attributes).build());
+            self.ops
+                .push(OperationBuilder::<T>::retain(n).attributes(attributes).build());
         }
     }
 
-    /// Applies an operation to a string, returning a new string.
-    pub fn apply(&self, s: &str) -> Result<String, OTError> {
-        let s: FlowyStr = s.into();
-        if s.utf16_size() != self.utf16_base_len {
+    /// Return the a new string described by this delta. The new string will contains the input string.
+    /// The length of the [applied_str] must be equal to the the [utf16_base_len].
+    ///
+    /// # Arguments
+    ///
+    /// * `applied_str`: A string represents the utf16_base_len content. it will be consumed by the [retain]
+    /// or [delete] operations.
+    ///
+    ///
+    /// # Examples
+    ///
+    /// ```
+    ///  use lib_ot::core::PlainTextDeltaBuilder;
+    ///  let s = "hello";
+    ///  let delta_a = PlainTextDeltaBuilder::new().insert(s).build();
+    ///  let delta_b = PlainTextDeltaBuilder::new()
+    ///         .retain(s.len())
+    ///         .insert(", AppFlowy")
+    ///         .build();
+    ///
+    ///  let after_a = delta_a.to_str().unwrap();
+    ///  let after_b = delta_b.apply(&after_a).unwrap();
+    ///  assert_eq!("hello, AppFlowy", &after_b);
+    /// ```
+    pub fn apply(&self, applied_str: &str) -> Result<String, OTError> {
+        let applied_str: FlowyStr = applied_str.into();
+        if applied_str.utf16_size() != self.utf16_base_len {
             return Err(ErrorBuilder::new(OTErrorCode::IncompatibleLength)
                 .msg(format!(
-                    "Expected: {}, received: {}",
+                    "Expected: {}, but received: {}",
                     self.utf16_base_len,
-                    s.utf16_size()
+                    applied_str.utf16_size()
                 ))
                 .build());
         }
         let mut new_s = String::new();
-        let code_point_iter = &mut s.utf16_code_unit_iter();
+        let code_point_iter = &mut applied_str.utf16_code_unit_iter();
         for op in &self.ops {
             match &op {
                 Operation::Retain(retain) => {
@@ -181,34 +219,60 @@ where
         Ok(new_s)
     }
 
-    /// Computes the inverse of an operation. The inverse of an operation is the
-    /// operation that reverts the effects of the operation
-    pub fn invert_str(&self, s: &str) -> Self {
+    /// Computes the inverse [Delta]. The inverse of an operation is the
+    /// operation that reverts the effects of the operation     
+    /// # Arguments
+    ///
+    /// * `inverted_s`: A string represents the utf16_base_len content. The len of [inverted_s]
+    /// must equal to the [utf16_base_len], it will be consumed by the [retain] or [delete] operations.
+    ///
+    /// If the delta's operations just contain a insert operation. The inverted_s must be empty string.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    ///  use lib_ot::core::PlainTextDeltaBuilder;
+    ///  let s = "hello world";
+    ///  let delta = PlainTextDeltaBuilder::new().insert(s).build();
+    ///  let invert_delta = delta.invert_str(s);
+    ///  assert_eq!(delta.utf16_base_len, invert_delta.utf16_target_len);
+    ///  assert_eq!(delta.utf16_target_len, invert_delta.utf16_base_len);
+    ///
+    ///  assert_eq!(invert_delta.apply(s).unwrap(), "")
+    ///
+    /// ```
+    ///
+    pub fn invert_str(&self, inverted_s: &str) -> Self {
         let mut inverted = Delta::default();
-        let chars = &mut s.chars();
+        let inverted_s: FlowyStr = inverted_s.into();
+        let code_point_iter = &mut inverted_s.utf16_code_unit_iter();
+
         for op in &self.ops {
             match &op {
                 Operation::Retain(retain) => {
                     inverted.retain(retain.n, T::default());
-                    // TODO: use advance_by instead, but it's unstable now
-                    // chars.advance_by(retain.num)
                     for _ in 0..retain.n {
-                        chars.next();
+                        code_point_iter.next();
                     }
                 }
                 Operation::Insert(insert) => {
                     inverted.delete(insert.utf16_size());
                 }
                 Operation::Delete(delete) => {
-                    inverted.insert(&chars.take(*delete as usize).collect::<String>(), op.get_attributes());
+                    let bytes = code_point_iter
+                        .take(*delete as usize)
+                        .into_iter()
+                        .flat_map(|a| str::from_utf8(a.0).ok())
+                        .collect::<String>();
+
+                    inverted.insert(&bytes, op.get_attributes());
                 }
             }
         }
         inverted
     }
 
-    /// Checks if this operation has no effect.
-    #[inline]
+    /// Return true if the delta doesn't contain any [Insert] or [Delete] operations.
     pub fn is_noop(&self) -> bool {
         matches!(self.ops.as_slice(), [] | [Operation::Retain(_)])
     }
@@ -231,8 +295,8 @@ where
         Self: Sized,
     {
         let mut new_delta = Delta::default();
-        let mut iter = DeltaIter::new(self);
-        let mut other_iter = DeltaIter::new(other);
+        let mut iter = DeltaIterator::new(self);
+        let mut other_iter = DeltaIterator::new(other);
 
         while iter.has_next() || other_iter.has_next() {
             if other_iter.is_next_insert() {
@@ -252,10 +316,10 @@ where
 
             let op = iter
                 .next_op_with_len(length)
-                .unwrap_or_else(|| OpBuilder::retain(length).build());
+                .unwrap_or_else(|| OperationBuilder::retain(length).build());
             let other_op = other_iter
                 .next_op_with_len(length)
-                .unwrap_or_else(|| OpBuilder::retain(length).build());
+                .unwrap_or_else(|| OperationBuilder::retain(length).build());
 
             // debug_assert_eq!(op.len(), other_op.len(), "Composing delta failed,");
 
@@ -263,12 +327,16 @@ where
                 (Operation::Retain(retain), Operation::Retain(other_retain)) => {
                     let composed_attrs = retain.attributes.compose(&other_retain.attributes)?;
 
-                    new_delta.add(OpBuilder::retain(retain.n).attributes(composed_attrs).build())
+                    new_delta.add(OperationBuilder::retain(retain.n).attributes(composed_attrs).build())
                 }
                 (Operation::Insert(insert), Operation::Retain(other_retain)) => {
                     let mut composed_attrs = insert.attributes.compose(&other_retain.attributes)?;
                     composed_attrs.remove_empty();
-                    new_delta.add(OpBuilder::insert(op.get_data()).attributes(composed_attrs).build())
+                    new_delta.add(
+                        OperationBuilder::insert(op.get_data())
+                            .attributes(composed_attrs)
+                            .build(),
+                    )
                 }
                 (Operation::Retain(_), Operation::Delete(_)) => {
                     new_delta.add(other_op);
@@ -331,7 +399,7 @@ where
                         Ordering::Less => {
                             a_prime.retain(retain.n, composed_attrs.clone());
                             b_prime.retain(retain.n, composed_attrs.clone());
-                            next_op2 = Some(OpBuilder::retain(o_retain.n - retain.n).build());
+                            next_op2 = Some(OperationBuilder::retain(o_retain.n - retain.n).build());
                             next_op1 = ops1.next();
                         }
                         Ordering::Equal => {
@@ -343,14 +411,14 @@ where
                         Ordering::Greater => {
                             a_prime.retain(o_retain.n, composed_attrs.clone());
                             b_prime.retain(o_retain.n, composed_attrs.clone());
-                            next_op1 = Some(OpBuilder::retain(retain.n - o_retain.n).build());
+                            next_op1 = Some(OperationBuilder::retain(retain.n - o_retain.n).build());
                             next_op2 = ops2.next();
                         }
                     };
                 }
                 (Some(Operation::Delete(i)), Some(Operation::Delete(j))) => match i.cmp(j) {
                     Ordering::Less => {
-                        next_op2 = Some(OpBuilder::delete(*j - *i).build());
+                        next_op2 = Some(OperationBuilder::delete(*j - *i).build());
                         next_op1 = ops1.next();
                     }
                     Ordering::Equal => {
@@ -358,7 +426,7 @@ where
                         next_op2 = ops2.next();
                     }
                     Ordering::Greater => {
-                        next_op1 = Some(OpBuilder::delete(*i - *j).build());
+                        next_op1 = Some(OperationBuilder::delete(*i - *j).build());
                         next_op2 = ops2.next();
                     }
                 },
@@ -366,7 +434,7 @@ where
                     match i.cmp(o_retain) {
                         Ordering::Less => {
                             a_prime.delete(*i);
-                            next_op2 = Some(OpBuilder::retain(o_retain.n - *i).build());
+                            next_op2 = Some(OperationBuilder::retain(o_retain.n - *i).build());
                             next_op1 = ops1.next();
                         }
                         Ordering::Equal => {
@@ -376,7 +444,7 @@ where
                         }
                         Ordering::Greater => {
                             a_prime.delete(o_retain.n);
-                            next_op1 = Some(OpBuilder::delete(*i - o_retain.n).build());
+                            next_op1 = Some(OperationBuilder::delete(*i - o_retain.n).build());
                             next_op2 = ops2.next();
                         }
                     };
@@ -385,7 +453,7 @@ where
                     match retain.cmp(j) {
                         Ordering::Less => {
                             b_prime.delete(retain.n);
-                            next_op2 = Some(OpBuilder::delete(*j - retain.n).build());
+                            next_op2 = Some(OperationBuilder::delete(*j - retain.n).build());
                             next_op1 = ops1.next();
                         }
                         Ordering::Equal => {
@@ -395,7 +463,7 @@ where
                         }
                         Ordering::Greater => {
                             b_prime.delete(*j);
-                            next_op1 = Some(OpBuilder::retain(retain.n - *j).build());
+                            next_op1 = Some(OperationBuilder::retain(retain.n - *j).build());
                             next_op2 = ops2.next();
                         }
                     };
@@ -407,21 +475,17 @@ where
 
     fn invert(&self, other: &Self) -> Self {
         let mut inverted = Delta::default();
-        if other.is_empty() {
-            return inverted;
-        }
-
         let mut index = 0;
         for op in &self.ops {
             let len: usize = op.len() as usize;
             match op {
                 Operation::Delete(n) => {
-                    invert_from_other(&mut inverted, other, op, index, index + *n);
+                    invert_other(&mut inverted, other, op, index, index + *n);
                     index += len;
                 }
                 Operation::Retain(_) => {
                     match op.has_attribute() {
-                        true => invert_from_other(&mut inverted, other, op, index, index + len),
+                        true => invert_other(&mut inverted, other, op, index, index + len),
                         false => {
                             // tracing::trace!("invert retain: {} by retain {} {}", op, len,
                             // op.get_attributes());
@@ -452,7 +516,7 @@ where
     }
 }
 
-fn invert_from_other<T: Attributes>(
+fn invert_other<T: Attributes>(
     base: &mut Delta<T>,
     other: &Delta<T>,
     operation: &Operation<T>,
@@ -460,7 +524,7 @@ fn invert_from_other<T: Attributes>(
     end: usize,
 ) {
     tracing::trace!("invert op: {} [{}:{}]", operation, start, end);
-    let other_ops = DeltaIter::from_interval(other, Interval::new(start, end)).ops();
+    let other_ops = DeltaIterator::from_interval(other, Interval::new(start, end)).ops();
     other_ops.into_iter().for_each(|other_op| match operation {
         Operation::Delete(_n) => {
             // tracing::trace!("invert delete: {} by add {}", n, other_op);
diff --git a/shared-lib/lib-ot/src/core/delta/delta_serde.rs b/shared-lib/lib-ot/src/core/delta/delta_serde.rs
index ceac31ee58..7dff063211 100644
--- a/shared-lib/lib-ot/src/core/delta/delta_serde.rs
+++ b/shared-lib/lib-ot/src/core/delta/delta_serde.rs
@@ -1,4 +1,5 @@
-use crate::core::{Attributes, Delta};
+use crate::core::delta::Delta;
+use crate::core::operation::Attributes;
 use serde::{
     de::{SeqAccess, Visitor},
     ser::SerializeSeq,
diff --git a/shared-lib/lib-ot/src/core/delta/iterator.rs b/shared-lib/lib-ot/src/core/delta/iterator.rs
index ccad56845d..ba9db58428 100644
--- a/shared-lib/lib-ot/src/core/delta/iterator.rs
+++ b/shared-lib/lib-ot/src/core/delta/iterator.rs
@@ -1,17 +1,17 @@
 use super::cursor::*;
-use crate::{
-    core::{Attributes, Delta, Interval, Operation, NEW_LINE},
-    rich_text::RichTextAttributes,
-};
+use crate::core::delta::{Delta, NEW_LINE};
+use crate::core::interval::Interval;
+use crate::core::operation::{Attributes, Operation};
+use crate::rich_text::RichTextAttributes;
 use std::ops::{Deref, DerefMut};
 
 pub(crate) const MAX_IV_LEN: usize = i32::MAX as usize;
 
-pub struct DeltaIter<'a, T: Attributes> {
-    cursor: OpCursor<'a, T>,
+pub struct DeltaIterator<'a, T: Attributes> {
+    cursor: DeltaCursor<'a, T>,
 }
 
-impl<'a, T> DeltaIter<'a, T>
+impl<'a, T> DeltaIterator<'a, T>
 where
     T: Attributes,
 {
@@ -28,7 +28,7 @@ where
     }
 
     pub fn from_interval(delta: &'a Delta<T>, interval: Interval) -> Self {
-        let cursor = OpCursor::new(delta, interval);
+        let cursor = DeltaCursor::new(delta, interval);
         Self { cursor }
     }
 
@@ -46,7 +46,7 @@ where
     }
 
     pub fn next_op(&mut self) -> Option<Operation<T>> {
-        self.cursor.next_op()
+        self.cursor.get_next_op()
     }
 
     pub fn next_op_with_len(&mut self, len: usize) -> Option<Operation<T>> {
@@ -80,28 +80,28 @@ where
     }
 
     pub fn is_next_insert(&self) -> bool {
-        match self.cursor.next_iter_op() {
+        match self.cursor.next_op() {
             None => false,
             Some(op) => op.is_insert(),
         }
     }
 
     pub fn is_next_retain(&self) -> bool {
-        match self.cursor.next_iter_op() {
+        match self.cursor.next_op() {
             None => false,
             Some(op) => op.is_retain(),
         }
     }
 
     pub fn is_next_delete(&self) -> bool {
-        match self.cursor.next_iter_op() {
+        match self.cursor.next_op() {
             None => false,
             Some(op) => op.is_delete(),
         }
     }
 }
 
-impl<'a, T> Iterator for DeltaIter<'a, T>
+impl<'a, T> Iterator for DeltaIterator<'a, T>
 where
     T: Attributes,
 {
@@ -112,7 +112,7 @@ where
 }
 
 pub fn is_empty_line_at_index(delta: &Delta<RichTextAttributes>, index: usize) -> bool {
-    let mut iter = DeltaIter::new(delta);
+    let mut iter = DeltaIterator::new(delta);
     let (prev, next) = (iter.next_op_with_len(index), iter.next_op());
     if prev.is_none() {
         return true;
@@ -128,7 +128,7 @@ pub fn is_empty_line_at_index(delta: &Delta<RichTextAttributes>, index: usize) -
 }
 
 pub struct AttributesIter<'a, T: Attributes> {
-    delta_iter: DeltaIter<'a, T>,
+    delta_iter: DeltaIterator<'a, T>,
 }
 
 impl<'a, T> AttributesIter<'a, T>
@@ -141,7 +141,7 @@ where
     }
 
     pub fn from_interval(delta: &'a Delta<T>, interval: Interval) -> Self {
-        let delta_iter = DeltaIter::from_interval(delta, interval);
+        let delta_iter = DeltaIterator::from_interval(delta, interval);
         Self { delta_iter }
     }
 
@@ -157,7 +157,7 @@ impl<'a, T> Deref for AttributesIter<'a, T>
 where
     T: Attributes,
 {
-    type Target = DeltaIter<'a, T>;
+    type Target = DeltaIterator<'a, T>;
 
     fn deref(&self) -> &Self::Target {
         &self.delta_iter
diff --git a/shared-lib/lib-ot/src/core/flowy_str.rs b/shared-lib/lib-ot/src/core/flowy_str.rs
index 95cc1735cc..9e503672eb 100644
--- a/shared-lib/lib-ot/src/core/flowy_str.rs
+++ b/shared-lib/lib-ot/src/core/flowy_str.rs
@@ -177,7 +177,7 @@ impl<'a> FlowyUtf16CodePointIterator<'a> {
     }
 }
 
-use crate::core::Interval;
+use crate::core::interval::Interval;
 use std::str;
 
 impl<'a> Iterator for FlowyUtf16CodePointIterator<'a> {
@@ -226,7 +226,8 @@ pub fn len_utf8_from_first_byte(b: u8) -> usize {
 
 #[cfg(test)]
 mod tests {
-    use crate::core::{FlowyStr, Interval};
+    use crate::core::flowy_str::FlowyStr;
+    use crate::core::interval::Interval;
 
     #[test]
     fn flowy_str_code_unit() {
diff --git a/shared-lib/lib-ot/src/core/interval.rs b/shared-lib/lib-ot/src/core/interval.rs
index a6f3131b6a..cc907ec3ea 100644
--- a/shared-lib/lib-ot/src/core/interval.rs
+++ b/shared-lib/lib-ot/src/core/interval.rs
@@ -157,7 +157,7 @@ impl From<RangeToInclusive<usize>> for Interval {
 
 #[cfg(test)]
 mod tests {
-    use crate::core::Interval;
+    use crate::core::interval::Interval;
 
     #[test]
     fn contains() {
diff --git a/shared-lib/lib-ot/src/core/mod.rs b/shared-lib/lib-ot/src/core/mod.rs
index b5bc594246..72a6dd9b74 100644
--- a/shared-lib/lib-ot/src/core/mod.rs
+++ b/shared-lib/lib-ot/src/core/mod.rs
@@ -3,28 +3,7 @@ mod flowy_str;
 mod interval;
 mod operation;
 
-use crate::errors::OTError;
 pub use delta::*;
 pub use flowy_str::*;
 pub use interval::*;
 pub use operation::*;
-
-pub trait OperationTransformable {
-    /// Merges the operation with `other` into one operation while preserving
-    /// the changes of both.
-    fn compose(&self, other: &Self) -> Result<Self, OTError>
-    where
-        Self: Sized;
-    /// Transforms two operations a and b that happened concurrently and
-    /// produces two operations a' and b'.
-    ///  (a', b') = a.transform(b)
-    ///  a.compose(b') = b.compose(a')
-    fn transform(&self, other: &Self) -> Result<(Self, Self), OTError>
-    where
-        Self: Sized;
-    /// Inverts the operation with `other` to produces undo operation.
-    /// undo = a.invert(b)
-    /// new_b = b.compose(a)
-    /// b = new_b.compose(undo)
-    fn invert(&self, other: &Self) -> Self;
-}
diff --git a/shared-lib/lib-ot/src/core/operation/builder.rs b/shared-lib/lib-ot/src/core/operation/builder.rs
index dc7b6dd7d9..a42ebdecb3 100644
--- a/shared-lib/lib-ot/src/core/operation/builder.rs
+++ b/shared-lib/lib-ot/src/core/operation/builder.rs
@@ -1,40 +1,38 @@
-use crate::{
-    core::{Attributes, Operation, PlainTextAttributes},
-    rich_text::RichTextAttributes,
-};
+use crate::core::operation::{Attributes, Operation, PlainTextAttributes};
+use crate::rich_text::RichTextAttributes;
 
-pub type RichTextOpBuilder = OpBuilder<RichTextAttributes>;
-pub type PlainTextOpBuilder = OpBuilder<PlainTextAttributes>;
+pub type RichTextOpBuilder = OperationBuilder<RichTextAttributes>;
+pub type PlainTextOpBuilder = OperationBuilder<PlainTextAttributes>;
 
-pub struct OpBuilder<T: Attributes> {
+pub struct OperationBuilder<T: Attributes> {
     ty: Operation<T>,
     attrs: T,
 }
 
-impl<T> OpBuilder<T>
+impl<T> OperationBuilder<T>
 where
     T: Attributes,
 {
-    pub fn new(ty: Operation<T>) -> OpBuilder<T> {
-        OpBuilder {
+    pub fn new(ty: Operation<T>) -> OperationBuilder<T> {
+        OperationBuilder {
             ty,
             attrs: T::default(),
         }
     }
 
-    pub fn retain(n: usize) -> OpBuilder<T> {
-        OpBuilder::new(Operation::Retain(n.into()))
+    pub fn retain(n: usize) -> OperationBuilder<T> {
+        OperationBuilder::new(Operation::Retain(n.into()))
     }
 
-    pub fn delete(n: usize) -> OpBuilder<T> {
-        OpBuilder::new(Operation::Delete(n))
+    pub fn delete(n: usize) -> OperationBuilder<T> {
+        OperationBuilder::new(Operation::Delete(n))
     }
 
-    pub fn insert(s: &str) -> OpBuilder<T> {
-        OpBuilder::new(Operation::Insert(s.into()))
+    pub fn insert(s: &str) -> OperationBuilder<T> {
+        OperationBuilder::new(Operation::Insert(s.into()))
     }
 
-    pub fn attributes(mut self, attrs: T) -> OpBuilder<T> {
+    pub fn attributes(mut self, attrs: T) -> OperationBuilder<T> {
         self.attrs = attrs;
         self
     }
diff --git a/shared-lib/lib-ot/src/core/operation/operation.rs b/shared-lib/lib-ot/src/core/operation/operation.rs
index 82228c19fc..8ff47d95e8 100644
--- a/shared-lib/lib-ot/src/core/operation/operation.rs
+++ b/shared-lib/lib-ot/src/core/operation/operation.rs
@@ -1,8 +1,9 @@
-use crate::{
-    core::{FlowyStr, Interval, OpBuilder, OperationTransformable},
-    errors::OTError,
-};
+use crate::core::flowy_str::FlowyStr;
+use crate::core::interval::Interval;
+use crate::core::operation::OperationBuilder;
+use crate::errors::OTError;
 use serde::{Deserialize, Serialize, __private::Formatter};
+use std::fmt::Display;
 use std::{
     cmp::min,
     fmt,
@@ -10,13 +11,73 @@ use std::{
     ops::{Deref, DerefMut},
 };
 
-pub trait Attributes: fmt::Display + Eq + PartialEq + Default + Clone + Debug + OperationTransformable {
-    fn is_empty(&self) -> bool;
+pub trait OperationTransformable {
+    /// Merges the operation with `other` into one operation while preserving
+    /// the changes of both.    
+    ///
+    /// # Arguments
+    ///
+    /// * `other`: The delta gonna to merge.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    ///  use lib_ot::core::{OperationTransformable, PlainTextDeltaBuilder};
+    ///  let document = PlainTextDeltaBuilder::new().build();
+    ///  let delta = PlainTextDeltaBuilder::new().insert("abc").build();
+    ///  let new_document = document.compose(&delta).unwrap();
+    ///  assert_eq!(new_document.to_str().unwrap(), "abc".to_owned());
+    /// ```
+    fn compose(&self, other: &Self) -> Result<Self, OTError>
+    where
+        Self: Sized;
 
-    // Remove the empty attribute which value is None.
-    fn remove_empty(&mut self);
+    /// Transforms two operations a and b that happened concurrently and
+    /// produces two operations a' and b'.
+    ///  (a', b') = a.transform(b)
+    ///  a.compose(b') = b.compose(a')    
+    ///
+    fn transform(&self, other: &Self) -> Result<(Self, Self), OTError>
+    where
+        Self: Sized;
 
-    fn extend_other(&mut self, other: Self);
+    /// Return the invert delta from the other. It can be used to do the undo operation.
+    ///
+    /// # Arguments
+    ///
+    /// * `other`:  Generate the undo delta for [Other]. [Other] can compose the undo delta to return
+    /// to the previous state.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use lib_ot::core::{OperationTransformable, PlainTextDeltaBuilder};
+    /// let original_document = PlainTextDeltaBuilder::new().build();
+    /// let delta = PlainTextDeltaBuilder::new().insert("abc").build();
+    ///
+    /// let undo_delta = delta.invert(&original_document);
+    /// let new_document = original_document.compose(&delta).unwrap();
+    /// let document = new_document.compose(&undo_delta).unwrap();
+    ///
+    /// assert_eq!(original_document, document);
+    ///
+    /// ```
+    fn invert(&self, other: &Self) -> Self;
+}
+
+pub trait Attributes: Default + Display + Eq + PartialEq + Clone + Debug + OperationTransformable {
+    fn is_empty(&self) -> bool {
+        true
+    }
+
+    /// Remove the empty attribute which value is None.
+    fn remove_empty(&mut self) {
+        // Do nothing
+    }
+
+    fn extend_other(&mut self, _other: Self) {
+        // Do nothing
+    }
 }
 
 #[derive(Debug, Clone, Eq, PartialEq)]
@@ -77,22 +138,22 @@ where
         let right;
         match self {
             Operation::Delete(n) => {
-                left = Some(OpBuilder::<T>::delete(index).build());
-                right = Some(OpBuilder::<T>::delete(*n - index).build());
+                left = Some(OperationBuilder::<T>::delete(index).build());
+                right = Some(OperationBuilder::<T>::delete(*n - index).build());
             }
             Operation::Retain(retain) => {
-                left = Some(OpBuilder::<T>::delete(index).build());
-                right = Some(OpBuilder::<T>::delete(retain.n - index).build());
+                left = Some(OperationBuilder::<T>::delete(index).build());
+                right = Some(OperationBuilder::<T>::delete(retain.n - index).build());
             }
             Operation::Insert(insert) => {
                 let attributes = self.get_attributes();
                 left = Some(
-                    OpBuilder::<T>::insert(&insert.s[0..index])
+                    OperationBuilder::<T>::insert(&insert.s[0..index])
                         .attributes(attributes.clone())
                         .build(),
                 );
                 right = Some(
-                    OpBuilder::<T>::insert(&insert.s[index..insert.utf16_size()])
+                    OperationBuilder::<T>::insert(&insert.s[index..insert.utf16_size()])
                         .attributes(attributes)
                         .build(),
                 );
@@ -104,16 +165,18 @@ where
 
     pub fn shrink(&self, interval: Interval) -> Option<Operation<T>> {
         let op = match self {
-            Operation::Delete(n) => OpBuilder::delete(min(*n, interval.size())).build(),
-            Operation::Retain(retain) => OpBuilder::retain(min(retain.n, interval.size()))
+            Operation::Delete(n) => OperationBuilder::delete(min(*n, interval.size())).build(),
+            Operation::Retain(retain) => OperationBuilder::retain(min(retain.n, interval.size()))
                 .attributes(retain.attributes.clone())
                 .build(),
             Operation::Insert(insert) => {
                 if interval.start > insert.utf16_size() {
-                    OpBuilder::insert("").build()
+                    OperationBuilder::insert("").build()
                 } else {
                     let s = insert.s.sub_str(interval).unwrap_or_else(|| "".to_owned());
-                    OpBuilder::insert(&s).attributes(insert.attributes.clone()).build()
+                    OperationBuilder::insert(&s)
+                        .attributes(insert.attributes.clone())
+                        .build()
                 }
             }
         };
@@ -212,7 +275,7 @@ where
             self.n += n;
             None
         } else {
-            Some(OpBuilder::retain(n).attributes(attributes).build())
+            Some(OperationBuilder::retain(n).attributes(attributes).build())
         }
     }
 
@@ -296,7 +359,7 @@ where
             self.s += s;
             None
         } else {
-            Some(OpBuilder::<T>::insert(s).attributes(attributes).build())
+            Some(OperationBuilder::<T>::insert(s).attributes(attributes).build())
         }
     }
 
@@ -346,15 +409,7 @@ impl fmt::Display for PlainTextAttributes {
     }
 }
 
-impl Attributes for PlainTextAttributes {
-    fn is_empty(&self) -> bool {
-        true
-    }
-
-    fn remove_empty(&mut self) {}
-
-    fn extend_other(&mut self, _other: Self) {}
-}
+impl Attributes for PlainTextAttributes {}
 
 impl OperationTransformable for PlainTextAttributes {
     fn compose(&self, _other: &Self) -> Result<Self, OTError> {
diff --git a/shared-lib/lib-ot/src/core/operation/operation_serde.rs b/shared-lib/lib-ot/src/core/operation/operation_serde.rs
index aefb909d0a..d029fb0e16 100644
--- a/shared-lib/lib-ot/src/core/operation/operation_serde.rs
+++ b/shared-lib/lib-ot/src/core/operation/operation_serde.rs
@@ -1,4 +1,5 @@
-use crate::core::{Attributes, FlowyStr, Insert, Operation, Retain};
+use crate::core::flowy_str::FlowyStr;
+use crate::core::operation::{Attributes, Insert, Operation, Retain};
 use serde::{
     de,
     de::{MapAccess, SeqAccess, Visitor},
diff --git a/shared-lib/lib-ot/src/rich_text/attributes.rs b/shared-lib/lib-ot/src/rich_text/attributes.rs
index d70e23228b..05d37317d2 100644
--- a/shared-lib/lib-ot/src/rich_text/attributes.rs
+++ b/shared-lib/lib-ot/src/rich_text/attributes.rs
@@ -1,10 +1,6 @@
 #![allow(non_snake_case)]
-use crate::{
-    block_attribute,
-    core::{Attributes, Operation, OperationTransformable},
-    errors::OTError,
-    ignore_attribute, inline_attribute, list_attribute,
-};
+use crate::core::{Attributes, Operation, OperationTransformable};
+use crate::{block_attribute, errors::OTError, ignore_attribute, inline_attribute, list_attribute};
 use lazy_static::lazy_static;
 use std::{
     collections::{HashMap, HashSet},
diff --git a/shared-lib/lib-ot/src/rich_text/delta.rs b/shared-lib/lib-ot/src/rich_text/delta.rs
index 99cb35f2bc..3a60cf7b02 100644
--- a/shared-lib/lib-ot/src/rich_text/delta.rs
+++ b/shared-lib/lib-ot/src/rich_text/delta.rs
@@ -1,7 +1,5 @@
-use crate::{
-    core::{Delta, DeltaBuilder},
-    rich_text::RichTextAttributes,
-};
+use crate::core::{Delta, DeltaBuilder};
+use crate::rich_text::RichTextAttributes;
 
 pub type RichTextDelta = Delta<RichTextAttributes>;
 pub type RichTextDeltaBuilder = DeltaBuilder<RichTextAttributes>;