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 
});
    it("should parse IRT/RT for a reply type", function (done) {
      const annotationRef = Ref.get(819, 0);
      const annotationDict = new Dict();
      annotationDict.set("Type", Name.get("Annot"));
      annotationDict.set("Subtype", Name.get("Text"));
      annotationDict.set("T", "ParentTitle");
      annotationDict.set("Contents", "ParentText");
      annotationDict.set("CreationDate", "D:20180423");
      annotationDict.set("M", "D:20190423");
      annotationDict.set("C", [0, 0, 1]);
      const pupRef = Ref.get(820, 0);
      const pupDict = new Dict();
      pupDict.set("Type", Name.get("Annot"));
      pupDict.set("Subtype", Name.get("Popup"));
      pupDict.set("Parent", annotationRef);
      annotationDict.set("Popup", pupRef);
      const replyRef = Ref.get(821, 0);
      const replyDict = new Dict();
      replyDict.set("Type", Name.get("Annot"));
      replyDict.set("Subtype", Name.get("Text"));
      replyDict.set("IRT", annotationRef);
      replyDict.set("RT", Name.get("R"));
      replyDict.set("T", "ReplyTitle");
      replyDict.set("Contents", "ReplyText");
      replyDict.set("CreationDate", "D:20180523");
      replyDict.set("M", "D:20190523");
      replyDict.set("C", [0.4]);
      const xref = new XRefMock([
        { ref: annotationRef, data: annotationDict },