In the following spots a "MouseUp" eventName is being used, which does look inconsistent considering that the "Mouse Down"/"Mouse Enter"/"Mouse Exit" eventNames all have a space in them.
Is this inconsistency actually expected, or is it a simple typo? If the former, then a comment explaining *why* would be appropriate; otherwise we should just fix this :-)

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L806

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L945

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L1034

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L1168

/cc @calixteman 
constructor(document, calculationOrder, objects) {
    this._document = document;
    this._calculationOrder = calculationOrder;
    this._objects = objects;
    this._document.obj._eventDispatcher = this;
  }
  mergeChange(event) {
    let value = event.value;
    if (typeof value !== "string") {
      value = value.toString();
    }
    const prefix =
      event.selStart >= 0 ? value.substring(0, event.selStart) : "";
    const postfix =
      event.selEnd >= 0 && event.selEnd <= value.length
        ? value.substring(event.selEnd)
        : "";
    return `${prefix}${event.change}${postfix}`;
  }
  dispatch(baseEvent) {
    const id = baseEvent.id;
    if (!(id in this._objects)) {
      let event;
      if (id === "doc" || id === "page") {
        event = globalThis.event = new Event(baseEvent);
        event.source = event.target = this._document.wrapped;
        event.name = baseEvent.name;
      }
      if (id === "doc") {
        this._document.obj._dispatchDocEvent(event.name);