diff --git a/src/api/converter.ts b/src/api/converter.ts
index 648f08a59..1fee5a158 100644
--- a/src/api/converter.ts
+++ b/src/api/converter.ts
@@ -277,12 +277,18 @@ function toTextNodeBoundary(
   switch (boundary?.getType()) {
     case BoundaryType.Before:
       pbTextNodeBoundary.setType(PbBoundaryType.BOUNDARY_TYPE_BEFORE);
+      break;
     case BoundaryType.After:
       pbTextNodeBoundary.setType(PbBoundaryType.BOUNDARY_TYPE_AFTER);
+      break;
     case BoundaryType.Start:
       pbTextNodeBoundary.setType(PbBoundaryType.BOUNDARY_TYPE_START);
+      break;
     case BoundaryType.End:
       pbTextNodeBoundary.setType(PbBoundaryType.BOUNDARY_TYPE_END);
+      break;
+    case BoundaryType.None:
+      pbTextNodeBoundary.setType(PbBoundaryType.BOUNDARY_TYPE_NONE);
   }
   return pbTextNodeBoundary;
 }
@@ -929,14 +935,18 @@ function fromTextNodeBoundary(
   switch (pbTextNodeBoundary.getType()) {
     case PbBoundaryType.BOUNDARY_TYPE_BEFORE:
       boundaryType = BoundaryType.Before;
+      break;
     case PbBoundaryType.BOUNDARY_TYPE_AFTER:
       boundaryType = BoundaryType.After;
+      break;
     case PbBoundaryType.BOUNDARY_TYPE_START:
       boundaryType = BoundaryType.Start;
+      break;
     case PbBoundaryType.BOUNDARY_TYPE_END:
       boundaryType = BoundaryType.End;
-    default:
-      boundaryType = undefined;
+      break;
+    case PbBoundaryType.BOUNDARY_TYPE_NONE:
+      boundaryType = BoundaryType.None;
   }
   return RGATreeSplitBoundary.of(
     RGATreeSplitNodeID.of(
diff --git a/src/api/yorkie/v1/resources.proto b/src/api/yorkie/v1/resources.proto
index 7e5bec2e3..65a1d2010 100644
--- a/src/api/yorkie/v1/resources.proto
+++ b/src/api/yorkie/v1/resources.proto
@@ -336,6 +336,7 @@ enum BoundaryType {
   BOUNDARY_TYPE_AFTER = 1;
   BOUNDARY_TYPE_START = 2;
   BOUNDARY_TYPE_END = 3;
+  BOUNDARY_TYPE_NONE = 4;
 }
 
 message TextNodeBoundary {
diff --git a/src/api/yorkie/v1/resources_pb.d.ts b/src/api/yorkie/v1/resources_pb.d.ts
index 0cf39e6a3..83f60acb0 100644
--- a/src/api/yorkie/v1/resources_pb.d.ts
+++ b/src/api/yorkie/v1/resources_pb.d.ts
@@ -1619,6 +1619,7 @@ export enum BoundaryType {
   BOUNDARY_TYPE_AFTER = 1,
   BOUNDARY_TYPE_START = 2,
   BOUNDARY_TYPE_END = 3,
+  BOUNDARY_TYPE_NONE = 4,
 }
 export enum ValueType { 
   VALUE_TYPE_NULL = 0,
diff --git a/src/api/yorkie/v1/resources_pb.js b/src/api/yorkie/v1/resources_pb.js
index 412fe75c9..01c1823a6 100644
--- a/src/api/yorkie/v1/resources_pb.js
+++ b/src/api/yorkie/v1/resources_pb.js
@@ -13407,7 +13407,8 @@ proto.yorkie.v1.BoundaryType = {
   BOUNDARY_TYPE_BEFORE: 0,
   BOUNDARY_TYPE_AFTER: 1,
   BOUNDARY_TYPE_START: 2,
-  BOUNDARY_TYPE_END: 3
+  BOUNDARY_TYPE_END: 3,
+  BOUNDARY_TYPE_NONE: 4
 };
 
 /**
diff --git a/src/document/crdt/rga_tree_split.ts b/src/document/crdt/rga_tree_split.ts
index bf18cc461..2172ae3ea 100644
--- a/src/document/crdt/rga_tree_split.ts
+++ b/src/document/crdt/rga_tree_split.ts
@@ -63,6 +63,8 @@ export enum BoundaryType {
   After = 'after',
   Start = 'start',
   End = 'end',
+  // TODO(MoonGyu1): 'None' type can be deleted after replacing existing logic with mark
+  None = 'none',
 }
 
 /**
@@ -415,10 +417,16 @@ export class RGATreeSplitNode<
     return this.insPrev!.getID();
   }
 
+  /**
+   * `getStyleOpsBefore` returns a styleOpsBefore of this node.
+   */
   public getStyleOpsBefore(): Set<StyleOperation> | undefined {
     return this.styleOpsBefore;
   }
 
+  /**
+   * `getStyleOpsAfter` returns a styleOpsAfter of this node.
+   */
   public getStyleOpsAfter(): Set<StyleOperation> | undefined {
     return this.styleOpsAfter;
   }
@@ -463,10 +471,16 @@ export class RGATreeSplitNode<
     }
   }
 
+  /**
+   * `setStyleOpsBefore` sets styleOpsBefore of this node.
+   */
   public setStyleOpsBefore(operations: Set<StyleOperation>): void {
     this.styleOpsBefore = operations;
   }
 
+  /**
+   * `setStyleOpsAfter` sets styleOpsAfter of this node.
+   */
   public setStyleOpsAfter(operations: Set<StyleOperation>): void {
     this.styleOpsAfter = operations;
   }
@@ -844,7 +858,7 @@ export class RGATreeSplit<T extends RGATreeSplitValue> {
   public splitNodeByBoundary(boundary: RGATreeSplitBoundary): void {
     const absoluteID = boundary.getID();
     if (absoluteID?.getCreatedAt()) {
-      let node = this.findFloorNodePreferToLeft(absoluteID);
+      const node = this.findFloorNodePreferToLeft(absoluteID);
       const relativeOffset = absoluteID.getOffset() - node.getID().getOffset();
 
       this.splitNode(node, relativeOffset);
diff --git a/src/document/crdt/text.ts b/src/document/crdt/text.ts
index 01cbb60ba..5a251d799 100644
--- a/src/document/crdt/text.ts
+++ b/src/document/crdt/text.ts
@@ -71,7 +71,7 @@ export type AttributeSpec = {
 export type MarkSpec = {
   expand: 'before' | 'after' | 'both' | 'none';
   allowMultiple: boolean;
-  excludes?: string[];
+  excludes?: Array<string>;
   attributes?: { [key: string]: AttributeSpec };
 };
 
@@ -272,7 +272,10 @@ export class CRDTText<A extends Indexable = Indexable> extends CRDTGCElement {
     const fromBoundary = range[0];
     const toBoundary = range[1];
     // 02-1. Update styleOpsBefore and styleOpsAfter if it is a bold type
-    if (fromBoundary.getType() && toBoundary?.getType()) {
+    if (
+      fromBoundary.getType() != BoundaryType.None &&
+      toBoundary?.getType() != BoundaryType.None
+    ) {
       // TODO(MoonGyu1): Peritext 2. Update styleOpsBefore/styleOpsAfter of fromRight/toRight nodes
 
       const createdAtMapByActor = new Map<string, TimeTicket>();
@@ -405,8 +408,8 @@ export class CRDTText<A extends Indexable = Indexable> extends CRDTGCElement {
     );
 
     return [
-      RGATreeSplitBoundary.of(fromRight.getID()),
-      RGATreeSplitBoundary.of(toRight?.getID()),
+      RGATreeSplitBoundary.of(fromRight.getID(), BoundaryType.None),
+      RGATreeSplitBoundary.of(toRight?.getID(), BoundaryType.None),
     ];
   }
 
diff --git a/src/document/json/text.ts b/src/document/json/text.ts
index 8d7ae03f6..40c476f4c 100644
--- a/src/document/json/text.ts
+++ b/src/document/json/text.ts
@@ -234,8 +234,12 @@ export class Text<A extends Indexable = Indexable> {
     return true;
   }
 
-  // TODO(MoonGyu1): Peritext 1. Add removeStyle method
-  removeStyle(fromIdx: number, toIdx: number, attributes: A) {}
+  /**
+   * `removeStyle` remove styles from text with the given attributes.
+   */
+  removeStyle(fromIdx: number, toIdx: number, attributes: A) {
+    // TODO(MoonGyu1): Peritext 1. Add removeStyle method
+  }
 
   /**
    * `indexRangeToPosRange` returns TextRangeStruct of the given index range.