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 
if (!url) {
    return false;
  }
  switch (url.protocol) {
    case "http:":
    case "https:":
    case "ftp:":
    case "mailto:":
    case "tel:":
      return true;
    default:
      return false;
  }
}
/**
 * Attempts to create a valid absolute URL.
 *
 * @param {URL|string} url - An absolute, or relative, URL.
 * @param {URL|string} baseUrl - An absolute URL.
 * @returns Either a valid {URL}, or `null` otherwise.
 */
function createValidAbsoluteUrl(url, baseUrl) {