diff --git a/src/components/DiagramFrame/SeqDiagram/LifeLineLayer/Participant.vue b/src/components/DiagramFrame/SeqDiagram/LifeLineLayer/Participant.vue
index 9315ae31..0c3c3da8 100644
--- a/src/components/DiagramFrame/SeqDiagram/LifeLineLayer/Participant.vue
+++ b/src/components/DiagramFrame/SeqDiagram/LifeLineLayer/Participant.vue
@@ -32,6 +32,7 @@
         :labelText="labelText"
         :labelPositions="labelPositions"
         :assignee="entity.assignee"
+        :assigneePositions="assigneePositions"
       />
     </div>
   </div>
@@ -63,9 +64,22 @@ export default {
       return { translate: 0, participant };
     }
 
-    const labelPositions = computed(() =>
-      store.getters.participants.Positions().get(props.entity.name),
-    );
+    const labelPositions = computed(() => {
+      const positions = store.getters.participants.GetPositions(
+        props.entity.name,
+      );
+      // Sort the label positions in descending order to avoid index shifting when updating code
+      const positionArray = Array.from(positions ?? []);
+      return positionArray.sort((a, b) => b[0] - a[0]);
+    });
+    const assigneePositions = computed(() => {
+      // Sort the label positions in descending order to avoid index shifting when updating code
+      const assigneePositions = store.getters.participants.GetAssigneePositions(
+        props.entity.name,
+      );
+      const positionArray = Array.from(assigneePositions ?? []);
+      return positionArray.sort((a, b) => b[0] - a[0]);
+    });
     const intersectionTop = useIntersectionTop();
     const [scrollTop] = useDocumentScroll();
     const translate = computed(() => {
@@ -86,7 +100,7 @@ export default {
         participantOffsetTop
       );
     });
-    return { translate, participant, labelPositions };
+    return { translate, participant, labelPositions, assigneePositions };
   },
   props: {
     entity: {
diff --git a/src/components/DiagramFrame/SeqDiagram/LifeLineLayer/ParticipantLabel.vue b/src/components/DiagramFrame/SeqDiagram/LifeLineLayer/ParticipantLabel.vue
index 779b8f7c..fdb0da99 100644
--- a/src/components/DiagramFrame/SeqDiagram/LifeLineLayer/ParticipantLabel.vue
+++ b/src/components/DiagramFrame/SeqDiagram/LifeLineLayer/ParticipantLabel.vue
@@ -1,19 +1,38 @@
 <template>
   <div class="flex items-center justify-center">
     <template v-if="assignee">
-      <label class="name leading-4">{{ assignee }}:</label>
+      <label
+        title="Double click to edit"
+        class="name leading-4 cursor-text right hover:text-skin-message-hover hover:bg-skin-message-hover"
+        :class="{
+          'py-1 cursor-text': assigneeLabelHandler.editing,
+        }"
+        :contenteditable="
+          assigneeLabelHandler.editing && mode === RenderMode.Dynamic
+        "
+        @dblclick="assigneeLabelHandler.handleDblClick"
+        @blur="assigneeLabelHandler.handleBlur"
+        @keyup="assigneeLabelHandler.handleKeyup"
+        @keydown="assigneeLabelHandler.handleKeydown"
+        >{{ assignee }}</label
+      >
+      <span>:</span>
     </template>
     <label
       title="Double click to edit"
       class="name leading-4 cursor-text right hover:text-skin-message-hover hover:bg-skin-message-hover"
       :class="{
-        'py-1 px-2 cursor-text': editing,
+        'py-1 cursor-text': participantLabelHandler.editing,
       }"
-      :contenteditable="editing && mode === RenderMode.Dynamic"
-      @dblclick="handleDblClick"
-      @blur="handleBlur"
-      @keyup="handleKeyup"
-      @keydown="handleKeydown"
+      :contenteditable="
+        participantLabelHandler.editing &&
+        mode === RenderMode.Dynamic &&
+        UneditableText.indexOf(labelText) === -1
+      "
+      @dblclick="participantLabelHandler.handleDblClick"
+      @blur="participantLabelHandler.handleBlur"
+      @keyup="participantLabelHandler.handleKeyup"
+      @keydown="participantLabelHandler.handleKeydown"
     >
       {{ labelText }}
     </label>
@@ -24,14 +43,19 @@ import { computed, toRefs } from "vue";
 import { useStore } from "vuex";
 import { useEditLabel, specialCharRegex } from "@/functions/useEditLabel";
 import { RenderMode } from "@/store/Store";
+import { Position } from "@/parser/Participants";
+
+const UneditableText = ["Missing Constructor", "ZenUML"];
 
 const props = defineProps<{
   labelText: string;
-  labelPositions?: Set<string>;
+  labelPositions?: Array<[number, number]>;
   assignee?: string;
+  assigneePositions?: Array<[number, number]>;
 }>();
 
-const { labelText, labelPositions } = toRefs(props);
+const { labelText, labelPositions, assigneePositions } = toRefs(props);
+
 const store = useStore();
 const mode = computed(() => store.state.mode);
 const code = computed(() => store.getters.code);
@@ -45,48 +69,48 @@ function updateCode(code: string) {
   onContentChange.value(code);
 }
 
-function replaceLabelText(e: Event) {
-  e.preventDefault();
-  e.stopPropagation();
-
-  const target = e.target;
-  if (!(target instanceof HTMLElement)) return;
-  let newText = target.innerText.trim() ?? "";
+function replaceLabelTextWithaPositions(positions: Array<Position>) {
+  return function (e: Event) {
+    e.preventDefault();
+    e.stopPropagation();
 
-  // If text is empty or same as the original label text,
-  // we replace it with the original label text and bail out early
-  if (newText === "" || newText === labelText.value) {
-    target.innerText = labelText.value;
-    return;
-  }
+    const target = e.target;
+    if (!(target instanceof HTMLElement)) return;
+    let newText = target.innerText.trim() ?? "";
 
-  if (newText.includes(" ")) {
-    newText = newText.replace(/\s+/g, " "); // remove extra spaces
-  }
+    // If text is empty or same as the original label text,
+    // we replace it with the original label text and bail out early
+    if (newText === "" || newText === labelText.value) {
+      target.innerText = labelText.value;
+      return;
+    }
 
-  // If text has special characters or space, we wrap it with double quotes
-  if (specialCharRegex.test(newText)) {
-    newText = newText.replace(/"/g, ""); // remove existing double quotes
-    newText = `"${newText}"`;
-    specialCharRegex.lastIndex = 0;
-  }
+    if (newText.includes(" ")) {
+      newText = newText.replace(/\s+/g, " "); // remove extra spaces
+    }
 
-  if (!labelPositions?.value) return;
+    // If text has special characters or space, we wrap it with double quotes
+    if (specialCharRegex.test(newText)) {
+      newText = newText.replace(/"/g, ""); // remove existing double quotes
+      newText = `"${newText}"`;
+      specialCharRegex.lastIndex = 0;
+    }
 
-  // Sort the label positions in descending order to avoid index shifting
-  const labelPositionsArray = Array.from(labelPositions.value);
-  const reversedSortedLabelPositions = labelPositionsArray.sort(
-    (a, b) => JSON.parse(b)[0] - JSON.parse(a)[0],
-  );
+    if (!positions || positions.length === 0) return;
 
-  let newCode = code.value;
-  for (const labelPosition of reversedSortedLabelPositions) {
-    const [start, end] = JSON.parse(labelPosition);
-    newCode = newCode.slice(0, start) + newText + newCode.slice(end);
-  }
-  updateCode(newCode);
+    let newCode = code.value;
+    for (const position of positions) {
+      const [start, end] = position;
+      newCode = newCode.slice(0, start) + newText + newCode.slice(end);
+    }
+    updateCode(newCode);
+  };
 }
 
-const { editing, handleDblClick, handleBlur, handleKeydown, handleKeyup } =
-  useEditLabel(replaceLabelText);
+const participantLabelHandler = useEditLabel(
+  replaceLabelTextWithaPositions(labelPositions?.value ?? []),
+);
+const assigneeLabelHandler = useEditLabel(
+  replaceLabelTextWithaPositions(assigneePositions?.value ?? []),
+);
 </script>
diff --git a/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Fragment/FragmentCritical.vue b/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Fragment/FragmentCritical.vue
index d006839a..deca4518 100644
--- a/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Fragment/FragmentCritical.vue
+++ b/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Fragment/FragmentCritical.vue
@@ -38,7 +38,7 @@
           :style="{ paddingLeft: `${offsetX}px` }"
           :context="blockInCritical"
           :selfCallIndent="selfCallIndent"
-          :number="`number`"
+          :number="number"
         ></block>
       </div>
     </div>
diff --git a/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Fragment/FragmentSection.vue b/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Fragment/FragmentSection.vue
index d8a752e6..6a2381bc 100644
--- a/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Fragment/FragmentSection.vue
+++ b/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Fragment/FragmentSection.vue
@@ -38,7 +38,7 @@
           :style="{ paddingLeft: `${offsetX}px` }"
           :context="blockInSection"
           :selfCallIndent="selfCallIndent"
-          :number="`number`"
+          :number="number"
         ></block>
       </div>
     </div>
diff --git a/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Interaction/Interaction.vue b/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Interaction/Interaction.vue
index 67a1d55a..dd65cfd7 100644
--- a/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Interaction/Interaction.vue
+++ b/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Interaction/Interaction.vue
@@ -29,7 +29,7 @@
       :classNames="messageClassNames"
       :textStyle="messageTextStyle"
       :context="message"
-      :number="`${number}`"
+      :number="number"
     />
     <message
       v-else
@@ -47,7 +47,7 @@
       :participant="to"
       :selfCallIndent="passOnOffset"
       :rtl="rightToLeft"
-      :number="`${number}`"
+      :number="number"
     />
     <message
       v-if="assignee && !isSelf"
diff --git a/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Interaction/SelfInvocation/SelfInvocation.vue b/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Interaction/SelfInvocation/SelfInvocation.vue
index 68b8b69c..cf7d92ce 100644
--- a/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Interaction/SelfInvocation/SelfInvocation.vue
+++ b/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Interaction/SelfInvocation/SelfInvocation.vue
@@ -61,6 +61,7 @@ const messageRef = ref();
 const labelPosition: ComputedRef<[number, number]> = computed(() => {
   // do not use .signature(). Multiple signatures are allowed, e.g. method().method1().method2()
   const func = context?.value.messageBody().func();
+  if (!func) return [-1, -1];
   return [func.start.start, func.stop.stop];
 });
 
diff --git a/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/InteractionAsync/Interaction-async.vue b/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/InteractionAsync/Interaction-async.vue
index 2553eea0..ab24c566 100644
--- a/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/InteractionAsync/Interaction-async.vue
+++ b/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/InteractionAsync/Interaction-async.vue
@@ -28,7 +28,7 @@
       :classNames="messageClassNames"
       :textStyle="messageTextStyle"
       :context="asyncMessage"
-      :number="`${number}`"
+      :number="number"
     />
     <message
       v-else
diff --git a/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Message/Message.vue b/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Message/Message.vue
index a182353b..11727926 100644
--- a/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Message/Message.vue
+++ b/src/components/DiagramFrame/SeqDiagram/MessageLayer/Block/Statement/Message/Message.vue
@@ -101,12 +101,12 @@ const labelText = computed(() => {
   switch (type?.value) {
     case "creation":
       // Extract the creation name from the content
-      return content?.value.match(creationRegex)?.[1];
+      return content?.value.match(creationRegex)?.[1] || "";
     case "sync":
     case "async":
     case "return":
     default:
-      return content?.value;
+      return content?.value || "";
   }
 });
 const labelPosition: ComputedRef<[number, number]> = computed(() => {
@@ -144,6 +144,9 @@ const labelPosition: ComputedRef<[number, number]> = computed(() => {
           [start, stop] = [ret?.start.start, ret?.stop.stop];
         } else if (context?.value instanceof sequenceParser.ContentContext) {
           [start, stop] = [context.value.start.start, context.value.stop.stop];
+        } else if (context?.value instanceof sequenceParser.AssignmentContext) {
+          const assignee = context.value.assignee();
+          [start, stop] = [assignee.start.start, assignee.stop.stop];
         }
       }
       break;
diff --git a/src/parser/Owner.js b/src/parser/Owner.js
index b4f8b1b0..7d136b15 100644
--- a/src/parser/Owner.js
+++ b/src/parser/Owner.js
@@ -9,6 +9,14 @@ CreationContext.prototype.Assignee = function () {
   return this.creationBody()?.assignment()?.assignee()?.getFormattedText();
 };
 
+CreationContext.prototype.AssigneePosition = function () {
+  const assignee = this.creationBody()?.assignment()?.assignee();
+  if (!assignee) {
+    return undefined;
+  }
+  return [assignee.start.start, assignee.stop.stop + 1];
+};
+
 CreationContext.prototype.Constructor = function () {
   return this.creationBody()?.construct()?.getFormattedText();
 };
diff --git a/src/parser/Participants.spec.ts b/src/parser/Participants.spec.ts
index c6055998..c53cc98e 100644
--- a/src/parser/Participants.spec.ts
+++ b/src/parser/Participants.spec.ts
@@ -1,15 +1,13 @@
-import { Participants } from "../parser/Participants";
+import { blankParticipant, Participants } from "../parser/Participants";
 
 describe("Participants", () => {
   test("Get implicitly declared participants", () => {
     const participants = new Participants();
     participants.Add("A");
-    expect(participants.ImplicitArray()).toEqual([
+    expect(participants.ImplicitArray().map((p) => p.ToValue())).toEqual([
       {
+        ...blankParticipant,
         name: "A",
-        isStarter: undefined,
-        stereotype: undefined,
-        width: undefined,
       },
     ]);
     expect(participants.Starter()).toBeUndefined();
@@ -21,16 +19,12 @@ describe("Participants", () => {
     participants.Add("A");
     expect(participants.ImplicitArray()).toEqual([
       {
+        ...blankParticipant,
         name: "B",
-        isStarter: undefined,
-        stereotype: undefined,
-        width: undefined,
       },
       {
+        ...blankParticipant,
         name: "A",
-        isStarter: undefined,
-        stereotype: undefined,
-        width: undefined,
       },
     ]);
     expect(participants.Starter()).toBeUndefined();
@@ -40,24 +34,22 @@ describe("Participants", () => {
     const participants = new Participants();
     participants.Add("A", { isStarter: true });
     expect(participants.Starter()).toEqual({
+      ...blankParticipant,
       name: "A",
       isStarter: true,
-      stereotype: undefined,
-      width: undefined,
     });
     participants.Add("A", {
+      ...blankParticipant,
       isStarter: false,
-      start: 1,
-      end: 2,
+      position: [1, 2],
       explicit: true,
     });
     expect(participants.Starter()).toEqual({
+      ...blankParticipant,
       name: "A",
       isStarter: true,
-      stereotype: undefined,
-      width: undefined,
       explicit: true,
+      positions: new Set([[1, 2]]),
     });
-    expect(participants.GetPositions("A")?.has("[1,2]"));
   });
 });
diff --git a/src/parser/Participants.ts b/src/parser/Participants.ts
index fc888885..c2335249 100644
--- a/src/parser/Participants.ts
+++ b/src/parser/Participants.ts
@@ -1,4 +1,3 @@
-import mergeWith from "lodash/mergeWith";
 export enum ParticipantType {
   Actor = 1,
   Boundary,
@@ -16,10 +15,10 @@ export enum ParticipantType {
   Undefined,
 }
 
+export type Position = [number, number];
+
 interface ParticipantOptions {
   isStarter?: boolean;
-  start?: number;
-  end?: number;
   stereotype?: string;
   width?: number;
   groupId?: number | string;
@@ -29,8 +28,25 @@ interface ParticipantOptions {
   color?: string;
   comment?: string;
   assignee?: string;
+  position?: Position;
+  assigneePosition?: Position;
 }
 
+export const blankParticipant = {
+  color: undefined,
+  comment: undefined,
+  explicit: undefined,
+  groupId: undefined,
+  isStarter: undefined,
+  label: undefined,
+  stereotype: undefined,
+  type: undefined,
+  width: undefined,
+  assignee: undefined,
+  positions: new Set(),
+  assigneePositions: new Set(),
+};
+
 export class Participant {
   name: string;
   private stereotype: string | undefined;
@@ -43,9 +59,15 @@ export class Participant {
   private color: string | undefined;
   private comment: string | undefined;
   private assignee: string | undefined;
+  positions: Set<Position> = new Set();
+  assigneePositions: Set<Position> = new Set();
 
   constructor(name: string, options: ParticipantOptions) {
     this.name = name;
+    this.mergeOptions(options);
+  }
+
+  public mergeOptions(options: ParticipantOptions) {
     const {
       stereotype,
       width,
@@ -58,16 +80,16 @@ export class Participant {
       comment,
       assignee,
     } = options;
-    this.stereotype = stereotype;
-    this.width = width;
-    this.groupId = groupId;
-    this.explicit = explicit;
-    this.isStarter = isStarter;
-    this.label = label;
-    this.type = type;
-    this.color = color;
-    this.comment = comment;
-    this.assignee = assignee;
+    this.stereotype ||= stereotype;
+    this.width ||= width;
+    this.groupId ||= groupId;
+    this.explicit ||= explicit;
+    this.isStarter ||= isStarter;
+    this.label ||= label;
+    this.type ||= type;
+    this.color ||= color;
+    this.comment ||= comment;
+    this.assignee ||= assignee;
   }
 
   public Type(): ParticipantType {
@@ -102,26 +124,49 @@ export class Participant {
     }
     return ParticipantType.Undefined;
   }
-}
 
-export type PositionStr<
-  A extends number = number,
-  B extends number = number,
-> = `[${A},${B}]`;
+  public AddPosition(position: Position) {
+    this.positions.add(position);
+  }
+
+  public ToValue() {
+    return {
+      name: this.name,
+      stereotype: this.stereotype,
+      width: this.width,
+      groupId: this.groupId,
+      explicit: this.explicit,
+      isStarter: this.isStarter,
+      label: this.label,
+      type: this.type,
+      color: this.color,
+      comment: this.comment,
+      assignee: this.assignee,
+      positions: this.positions,
+      assigneePositions: this.assigneePositions,
+    };
+  }
+}
 
 export class Participants {
   private participants = new Map<string, Participant>();
-  private participantPositions = new Map<string, Set<PositionStr>>();
 
   public Add(name: string, options: ParticipantOptions = {}): void {
-    const participant = new Participant(name, options);
-    this.participants.set(
-      name,
-      mergeWith({}, this.Get(name), participant, (a, b) => a || b),
-    );
-    const { start, end } = options;
-    if (start !== undefined && end !== undefined) {
-      this.addPosition(name, start, end);
+    let participant = this.Get(name);
+    if (!participant) {
+      participant = new Participant(name, options);
+      this.participants.set(name, participant);
+    } else {
+      participant?.mergeOptions(options);
+    }
+
+    // Add positions
+    const { position, assigneePosition } = options;
+    if (position) {
+      participant.AddPosition(position);
+    }
+    if (assigneePosition) {
+      participant.assigneePositions.add(assigneePosition);
     }
   }
 
@@ -158,24 +203,14 @@ export class Participants {
   Starter() {
     const first = this.First();
     // const type = first.name === 'User' || first.name === 'Actor' ? 'actor' : undefined;
-    return first.isStarter ? first : undefined;
-  }
-
-  Positions() {
-    return this.participantPositions;
+    return first?.isStarter ? first : undefined;
   }
 
   GetPositions(name: string) {
-    return this.participantPositions.get(name);
+    return this.participants.get(name)?.positions;
   }
 
-  private addPosition(name: string, start: number, end: number) {
-    let positions = this.participantPositions.get(name);
-    if (!positions) {
-      positions = new Set();
-      this.participantPositions.set(name, positions);
-    }
-
-    positions.add(`[${start},${end}]`);
+  GetAssigneePositions(name: string) {
+    return this.participants.get(name)?.assigneePositions;
   }
 }
diff --git a/src/parser/SignatureText.ts b/src/parser/SignatureText.ts
index 82060846..12f52be2 100644
--- a/src/parser/SignatureText.ts
+++ b/src/parser/SignatureText.ts
@@ -24,8 +24,8 @@ AsyncMessageContext.prototype.SignatureText = function () {
 // @ts-ignore
 CreationContext.prototype.SignatureText = function () {
   const params = this.creationBody().parameters();
-  // @ts-ignore
   const text =
+    // @ts-ignore
     params?.parameter()?.length > 0 ? params.getFormattedText() : "create";
   return "«" + text + "»";
 };
diff --git a/src/parser/ToCollector.js b/src/parser/ToCollector.js
index 183aab48..4acd701a 100644
--- a/src/parser/ToCollector.js
+++ b/src/parser/ToCollector.js
@@ -1,8 +1,8 @@
 import { Participants } from "./Participants";
-
 import antlr4 from "antlr4";
 import { default as sequenceParserListener } from "../generated-parser/sequenceParserListener";
 import { default as sequenceParser } from "../generated-parser/sequenceParser";
+
 const seqParser = sequenceParser;
 const ProgContext = seqParser.ProgContext;
 
@@ -14,7 +14,7 @@ const ToCollector = new sequenceParserListener();
 // Rules:
 // 1. Later declaration win
 // 2. Participant declaration overwrite cannot be overwritten by To or Starter
-let onParticipant = function (ctx) {
+const onParticipant = function (ctx) {
   // if(!(ctx?.name())) return;
   if (isBlind) return;
   const type = ctx?.participantType()?.getFormattedText().replace("@", "");
@@ -46,8 +46,6 @@ let onParticipant = function (ctx) {
 
   participants.Add(participant, {
     isStarter: false,
-    start,
-    end,
     type,
     stereotype,
     width,
@@ -56,11 +54,12 @@ let onParticipant = function (ctx) {
     explicit,
     color,
     comment,
+    position: [start, end],
   });
 };
 ToCollector.enterParticipant = onParticipant;
 
-let onTo = function (ctx) {
+const onTo = function (ctx) {
   if (isBlind) return;
   let participant = ctx.getFormattedText();
   const participantInstance = participants.Get(participant);
@@ -71,17 +70,22 @@ let onTo = function (ctx) {
   } else if (participantInstance?.assignee) {
     // If the participant has an assignee, calculate the position of the ctor and store it only.
     // Let's say the participant name is `"${assignee}:${type}"`, we need to get the position of ${type}
+    // e.g. ret = new A() "ret:A".method()
     const start = ctx.start.start + participantInstance.assignee.length + 2;
+    const position = [start, ctx.stop.stop];
+    const assigneePosition = [
+      ctx.start.start + 1,
+      ctx.start.start + participantInstance.assignee.length + 1,
+    ];
     participants.Add(participant, {
       isStarter: false,
-      start: start,
-      end: ctx.stop.stop,
+      position: position,
+      assigneePosition: assigneePosition,
     });
   } else {
     participants.Add(participant, {
       isStarter: false,
-      start: ctx.start.start,
-      end: ctx.stop.stop + 1,
+      position: [ctx.start.start, ctx.stop.stop + 1],
     });
   }
 };
@@ -93,8 +97,7 @@ ToCollector.enterStarter = function (ctx) {
   let participant = ctx.getFormattedText();
   participants.Add(participant, {
     isStarter: true,
-    start: ctx.start.start,
-    end: ctx.stop.stop + 1,
+    position: [ctx.start.start, ctx.stop.stop + 1],
   });
 };
 
@@ -106,14 +109,17 @@ ToCollector.enterCreation = function (ctx) {
   // Skip adding participant constructor position if label is present
   if (ctor && !participantInstance?.label) {
     const assignee = ctx.Assignee();
+    const assigneePosition = ctx.AssigneePosition();
     participants.Add(participant, {
       isStarter: false,
-      start: ctor.start.start,
-      end: ctor.stop.stop + 1,
+      position: [ctor.start.start, ctor.stop.stop + 1],
       assignee: assignee,
+      assigneePosition: assigneePosition,
     });
   } else {
-    participants.Add(participant, { isStarter: false });
+    participants.Add(participant, {
+      isStarter: false,
+    });
   }
 };
 
diff --git a/test/unit/parser/to-collector.spec.js b/test/unit/parser/to-collector.spec.js
index 01c77fc0..a52f4d1b 100644
--- a/test/unit/parser/to-collector.spec.js
+++ b/test/unit/parser/to-collector.spec.js
@@ -2,6 +2,7 @@ import { Fixture } from "./fixture/Fixture";
 import { RootContext } from "../../../src/parser/index";
 import ToCollector from "../../../src/parser/ToCollector";
 import { expect } from "vitest";
+import { blankParticipant } from "../../../src/parser/Participants";
 
 test("smoke test2", () => {
   const code = `
@@ -14,17 +15,19 @@ test("smoke test2", () => {
     new F
   `;
   let participants = getParticipants(code);
-  expect(participants.Get("B 1")).toEqual({
+  const participant = participants.Get("B 1");
+  expect(participant.ToValue()).toEqual({
+    ...blankParticipant,
     name: "B 1",
     comment: " comment\n",
-    color: undefined,
-    label: undefined,
     isStarter: true,
     explicit: true,
-    groupId: undefined,
     stereotype: "A",
     width: 1024,
-    type: undefined,
+    positions: new Set([
+      [32, 37],
+      [56, 61],
+    ]),
   });
 });
 
@@ -108,7 +111,7 @@ describe("with label", () => {
   });
   test("participant position with label", () => {
     let participants = getParticipants("A as AA A.method", true);
-    expect(participants.GetPositions("A")).toEqual(new Set(["[5,7]"]));
+    expect(participants.GetPositions("A")).toEqual(new Set([[5, 7]]));
   });
 });
 
@@ -138,7 +141,7 @@ describe("Add Starter to participants", () => {
     expect(participants.Size()).toBe(1);
     expect(participants.Get("_STARTER_").name).toBe("_STARTER_");
     expect(participants.Get("_STARTER_").isStarter).toBeTruthy();
-    expect(participants.GetPositions("_STARTER_")).toBeUndefined();
+    expect(participants.GetPositions("_STARTER_")).toEqual(new Set());
   });
 
   test("A B->A.m", () => {
@@ -155,24 +158,19 @@ describe("implicit", () => {
   describe("from new", () => {
     test("from new", () => {
       let participants = getParticipants("new A()", true);
-      expect(participants.Get("A")).toEqual({
-        color: undefined,
-        comment: undefined,
-        explicit: undefined,
-        groupId: undefined,
-        isStarter: false,
-        label: undefined,
+      const participant = participants.Get("A");
+      expect(participant.ToValue()).toEqual({
+        ...blankParticipant,
         name: "A",
-        stereotype: undefined,
-        type: undefined,
-        width: undefined,
+        isStarter: false,
+        positions: new Set([[4, 5]]),
       });
     });
     test("seqDsl should treat creation as a participant - assignment", () => {
       let participants = getParticipants("a = new A()", true);
       expect(participants.Size()).toBe(2);
       expect(participants.Get("a:A").width).toBeUndefined();
-      expect(participants.GetPositions("a:A")).toEqual(new Set(["[8,9]"]));
+      expect(participants.GetPositions("a:A")).toEqual(new Set([[8, 9]]));
     });
     test("seqDsl should treat creation as a participant - assignment with type", () => {
       // We need @Starter, otherwise IA becomes a participant declaration
@@ -181,8 +179,8 @@ describe("implicit", () => {
       expect(participants.Get("X").width).toBeUndefined();
       expect(participants.Get("a:A").width).toBeUndefined();
       expect(participants.GetPositions("X").size).toBe(1);
-      expect(participants.GetPositions("X")).toEqual(new Set(["[9,10]"]));
-      expect(participants.GetPositions("a:A")).toEqual(new Set(["[23,24]"]));
+      expect(participants.GetPositions("X")).toEqual(new Set([[9, 10]]));
+      expect(participants.GetPositions("a:A")).toEqual(new Set([[23, 24]]));
     });
 
     test("seqDsl should treat creation as a participant - assignment & method call ", () => {
@@ -193,7 +191,10 @@ describe("implicit", () => {
       expect(participants.Size()).toBe(2);
       expect(participants.Get("ret:A").width).toBeUndefined();
       expect(participants.GetPositions("ret:A")).toEqual(
-        new Set(["[10,11]", "[19,20]"]),
+        new Set([
+          [10, 11],
+          [19, 20],
+        ]),
       );
     });
   });
@@ -201,36 +202,31 @@ describe("implicit", () => {
   describe("from method call", () => {
     test("get participants", () => {
       const participants = getParticipants("A.method", true);
-      expect(participants.Get("A")).toEqual({
-        color: undefined,
-        comment: undefined,
-        explicit: undefined,
-        groupId: undefined,
-        isStarter: false,
-        label: undefined,
+      const participant = participants.Get("A");
+      expect(participant.ToValue()).toEqual({
+        ...blankParticipant,
         name: "A",
-        stereotype: undefined,
-        type: undefined,
-        width: undefined,
+        isStarter: false,
+        positions: new Set([[0, 1]]),
       });
     });
     test("seqDsl should get all participants but ignore parameters - method call", () => {
       let participants = getParticipants('"b:B".method(x.m)', true);
       expect(participants.Size()).toBe(2);
       expect(participants.Get("b:B").width).toBeUndefined();
-      expect(participants.GetPositions("b:B")).toEqual(new Set(["[0,5]"]));
+      expect(participants.GetPositions("b:B")).toEqual(new Set([[0, 5]]));
     });
     test("seqDsl should get all participants but ignore parameters - creation", () => {
       let participants = getParticipants('"b:B".method(new X())', true);
       expect(participants.Size()).toBe(2);
       expect(participants.Get("b:B").width).toBeUndefined();
-      expect(participants.GetPositions("b:B")).toEqual(new Set(["[0,5]"]));
+      expect(participants.GetPositions("b:B")).toEqual(new Set([[0, 5]]));
     });
     test("seqDsl should get all participants including from", () => {
       let participants = getParticipants("A->B.m", true);
       expect(participants.Size()).toBe(2);
-      expect(participants.GetPositions("A")).toEqual(new Set(["[0,1]"]));
-      expect(participants.GetPositions("B")).toEqual(new Set(["[3,4]"]));
+      expect(participants.GetPositions("A")).toEqual(new Set([[0, 1]]));
+      expect(participants.GetPositions("B")).toEqual(new Set([[3, 4]]));
     });
   });
 
@@ -256,7 +252,8 @@ describe("implicit", () => {
         "B",
         "A",
       ]);
-      expect(participants.Positions().size).toEqual(2);
+      expect(participants.GetPositions("A").size).toEqual(1);
+      expect(participants.GetPositions("B").size).toEqual(1);
     });
 
     test("seqDsl should get all participants from a node of the root context", () => {
@@ -279,7 +276,8 @@ describe("implicit", () => {
         "D",
         "C",
       ]);
-      expect(participants.Positions().size).toEqual(0);
+      expect(participants.GetPositions("C").size).toEqual(0);
+      expect(participants.GetPositions("D").size).toEqual(0);
     });
   });
 });