onMouseMove(event) {
    const pointer = this.getPointer({ x: event.clientX, y: event.clientY });
    let popupVisible = false;

    // check if the previously selected node is still selected
    if (this.popup !== undefined) {
      if (this.popup.hidden === false) {
        this._checkHidePopup(pointer);
      }

      // if the popup was not hidden above
      if (this.popup.hidden === false) {
        popupVisible = true;
        this.popup.setPosition(pointer.x + 3, pointer.y - 5);
        this.popup.show();
      }
    }

    // if we bind the keyboard to the div, we have to highlight it to use it. This highlights it on mouse over.
    if (
      this.options.keyboard.autoFocus &&
      this.options.keyboard.bindToWindow === false &&
      this.options.keyboard.enabled === true
    ) {
      this.canvas.frame.focus();
    }

    // start a timeout that will check if the mouse is positioned above an element
    if (popupVisible === false) {
      if (this.popupTimer !== undefined) {
        clearInterval(this.popupTimer); // stop any running calculationTimer
        this.popupTimer = undefined;
      }
      if (!this.drag.dragging) {
        this.popupTimer = setTimeout(
          () => this._checkShowPopup(pointer),
          this.options.tooltipDelay
        );
      }
    }

    // adding hover highlights
    if (this.options.hover === true) {
      this.selectionHandler.hoverObject(event, pointer);
    }
  }
Mouse move handler for checking whether the title moves over a node with a title.
@param  {Event} event
@private