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 
}
      element.disabled = this.data.readOnly;
      element.name = this.data.fieldName;
      if (this.data.maxLen !== null) {
        element.maxLength = this.data.maxLen;
      }
      if (this.data.comb) {
        const fieldWidth = this.data.rect[2] - this.data.rect[0];
        const combWidth = fieldWidth / this.data.maxLen;
        element.classList.add("comb");
        element.style.letterSpacing = `calc(${combWidth}px - 1ch)`;
      }
    } else {
      element = document.createElement("div");
      element.textContent = this.data.fieldValue;
      element.style.verticalAlign = "middle";
      element.style.display = "table-cell";
    }
    this._setTextStyle(element);
    this.container.appendChild(element);
    return this.container;
  }
  /**
   * Apply text styles to the text in the element.
   *
   * @private
   * @param {HTMLDivElement} element
   * @memberof TextWidgetAnnotationElement
   */
  _setTextStyle(element) {