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 
const TEXT_ALIGNMENT = ["left", "center", "right"];
    const { fontSize, fontColor } = this.data.defaultAppearanceData;
    const style = element.style;
    
    
    
    if (fontSize) {
      style.fontSize = `${fontSize}px`;
    }
    style.color = Util.makeHexColor(fontColor[0], fontColor[1], fontColor[2]);
    if (this.data.textAlignment !== null) {
      style.textAlign = TEXT_ALIGNMENT[this.data.textAlignment];
    }
  }
}
class CheckboxWidgetAnnotationElement extends WidgetAnnotationElement {