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 
/* Copyright 2012 Mozilla Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import "./compatibility.js";
const IDENTITY_MATRIX = [1, 0, 0, 1, 0, 0];
const FONT_IDENTITY_MATRIX = [0.001, 0, 0, 0.001, 0, 0];
const PermissionFlag = {
  PRINT: 0x04,
  MODIFY_CONTENTS: 0x08,
  COPY: 0x10,
  MODIFY_ANNOTATIONS: 0x20,
  FILL_INTERACTIVE_FORMS: 0x100,
  COPY_FOR_ACCESSIBILITY: 0x200,
  ASSEMBLE: 0x400,
  PRINT_HIGH_QUALITY: 0x800,
};
const TextRenderingMode = {
  FILL: 0,
  STROKE: 1,