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 
writable: false,
        enumerable: true,
        value: event.value,
      });
    } else if (name === "Validate") {
      this.runValidation(source, event);
      return;
    }
    this.runActions(source, source, event, name);
    if (name === "Keystroke") {
      if (event.rc) {
        if (event.willCommit) {
          this.runValidation(source, event);
        } else if (
          event.change !== savedChange.change ||
          event.selStart !== savedChange.selStart ||
          event.selEnd !== savedChange.selEnd
        ) {
          source.wrapped.value = this.mergeChange(event);
        }
      } else if (!event.willCommit) {
        source.obj._send({
          id: source.obj._id,
          value: savedChange.value,
          selRange: [savedChange.selStart, savedChange.selEnd],
        });
      }
    }
  }
  runValidation(source, event) {