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(msg, code) {
    super(msg);
    this.code = code;
  }
}
class UnknownErrorException extends BaseException {
  constructor(msg, details) {
    super(msg);
    this.details = details;
  }
}
class InvalidPDFException extends BaseException {}
class MissingPDFException extends BaseException {}
class UnexpectedResponseException extends BaseException {
  constructor(msg, status) {
    super(msg);
    this.status = status;
  }
}
/**
 * Error caused during parsing PDF data.
 */
class FormatError extends BaseException {}
/**
 * Error used to indicate task cancellation.
 */
class AbortException extends BaseException {}