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 
"Lorem ipsum dolor sit amet, consectetur adipiscing elit.\r" +
              "Aliquam vitae felis ac lectus bibendum ultricies quis non diam.\n" +
              "Morbi id rttitor quam, a iaculis dui.\r\n" +
              "Pellentesque habitant morbi tristique senectus et " +
              "netus et malesuada fames ac turpis egestas.\n\r\n\r" +
              "Nulla consectetur, ligula in tincidunt placerat, " +
              "velit augue consectetur orci, sed mattis libero nunc ut massa.\r" +
              "Etiam facilisis tempus interdum.",
          };
          return annotation._getAppearance(
            partialEvaluator,
            task,
            annotationStorage
          );
        }, done.fail)
        .then(appearance => {
          expect(appearance).toEqual(expectedAppearance);
          done();
        }, done.fail);
    });
    it("should render comb for printing", function (done) {
      textWidgetDict.set("Ff", AnnotationFieldFlag.COMB);
      textWidgetDict.set("MaxLen", 4);
      const textWidgetRef = Ref.get(271, 0);
      const xref = new XRefMock([
        { ref: textWidgetRef, data: textWidgetDict },
        helvRefObj,
      ]);
      const task = new WorkerTask("test print");
      partialEvaluator.xref = xref;