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 
isSameOrigin,
  isString,
  MissingPDFException,
  objectFromEntries,
  objectSize,
  OPS,
  PageActionEventType,
  PasswordException,
  PasswordResponses,
  PermissionFlag,
  removeNullCharacters,
  setVerbosityLevel,
  shadow,
  StreamType,
  string32,
  stringToBytes,
  stringToPDFString,
  stringToUTF16BEString,
  stringToUTF8String,
  TextRenderingMode,
  UnexpectedResponseException,
  UnknownErrorException,
  unreachable,
  UNSUPPORTED_FEATURES,
  utf8StringToString,
  Util,
  VerbosityLevel,
  warn,
};