function isOutside(mouseEvent) {
        if (mouseEvent.clientY < Math.floor(bounds.top)) {
          return true;
        }

        if (mouseEvent.clientY > Math.ceil(bounds.top + bounds.height)) {
          return true;
        }

        if (mouseEvent.clientX < Math.floor(bounds.left)) {
          return true;
        }

        if (mouseEvent.clientX > Math.ceil(bounds.left + bounds.width)) {
          return true;
        }
      }
Mouse enter listener for fragment selection functionality.

@private
@param {Event} event Dom event
@param {HTMLElement} parentElement Part of border element.